Clarity Test checklist →

The approach · step one

Is this an evidence-based way to think about skin?

Short answer: in parts, strongly — in parts, it is early and honestly labelled as such. This page explains the lens and shows you exactly how to read the grades before you trust any of it.

Clarity treats a skin condition as a possible signal of upstream physiology rather than an isolated, fixed fact. That is a hypothesis-generating lens — a structured way to ask better questions with your clinician. It is explicitly not a treatment protocol, not a diagnosis, and not a cure claim. Every published page passes a human review gate before it goes live.

Read the evidence grades

What the badges mean.

Grades describe how strong the underlying literature is — never whether something is good or bad for you. Saturation, not colour, carries the signal; the label is always present.

Grade A

Strongest

Meta-analysis / RCT

Grade B

Solid

Cohort / observational

Grade C

Emerging

Mechanistic / animal

Grade D

Early

Hypothesis / opinion

An abstract-level tag means no open-access full text underpins the claim — the finding rests on an abstract alone, so read it more cautiously.

The eight-system primer

How each system enters the picture.

A condition-agnostic primer: the plausible mechanism for each system, with its evidence graded honestly. Per-condition specifics live on each condition’s pages.

  1. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A broad and converging body of evidence — spanning randomised controlled trials of probiotic and prebiotic interventions, mechanistic reviews of short-chain fatty acid signalling, and clinical studies of faecal microbiota transplantation — demonstrates that the gut microbiome communicates bidirectionally with distal organ systems, including the skin, through immune modulation, metabolite trafficking, and barrier regulation, establishing the gut microbiome as a biologically grounded systemic lens on inflammatory and barrier-related skin biology.

    doi:10.1016/j.jare.2025.12.032 · doi:10.1007/s12026-024-09484-7 · doi:10.1136/rmdopen-2023-003750 · doi:10.3390/ijms242115644 · doi:10.3390/nu15081982 · doi:10.1186/s12915-023-01531-3 · doi:10.3389/fimmu.2022.1009304 · doi:10.3390/foods11182863 · doi:10.3390/microorganisms10071428 · doi:10.4161/gmic.25487

  2. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A substantial and growing body of evidence — spanning bibliometric analyses, mechanistic reviews, randomised controlled trials of oral probiotics and prebiotics, and observational microbiome studies — establishes the gut microbiome as a biologically credible lens on skin biology, operating through immune modulation, microbial metabolite signalling (including short-chain fatty acids and phenolic compounds), and intestinal barrier integrity to influence cutaneous homeostasis across a range of skin states and conditions.

    doi:10.3389/fcimb.2026.1800070 · doi:10.1016/j.tice.2026.103534 · doi:10.1007/s11357-026-02211-0 · doi:10.2147/CCID.S571984 · doi:10.3390/molecules30224363 · doi:10.3390/nu17182976 · doi:10.3390/life15091434 · doi:10.1007/s00203-025-04267-6 · doi:10.1096/fj.202401478RR · doi:10.1016/j.arr.2024.102518 · doi:10.1016/j.nut.2024.112533 · doi:10.3390/nu15143123 · doi:10.3390/ijms232113071 · doi:10.3390/nu13124550 · doi:10.3390/nu12123673 · doi:10.1371/journal.pone.0231268 · doi:10.3920/BM2017.0091 · doi:10.3920/BM2012.0066

  3. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A broad body of narrative and mechanistic reviews documents how gut microbial composition, diversity, and metabolite output — particularly short-chain fatty acids, tryptophan derivatives, and bile acids — regulate epithelial barrier integrity and systemic immune tone across multiple barrier surfaces including the skin, gut, and lung, with an EAACI position paper providing grade-A support for dietary fibre as a lever on this axis.

    doi:10.5415/apallergy.0000000000000262 · doi:10.3390/life16030433 · doi:10.1038/s12276-026-01642-1 · doi:10.3390/nu17182925 · doi:10.1016/j.jaip.2025.04.041 · doi:10.3390/nu17061014 · doi:10.1111/all.16092 · doi:10.1002/clt2.12339 · doi:10.1016/j.cbi.2023.110739 · doi:10.3390/nu15173683 · doi:10.3390/nu15112529 · doi:10.18176/jiaci.0852 · doi:10.1111/all.15430 · doi:10.1007/s11882-021-01020-z · doi:10.1097/MOG.0000000000000780 · doi:10.1016/j.anai.2020.07.013 · doi:10.3389/fimmu.2020.00700 · doi:10.1172/JCI124610 · doi:10.1016/j.immuni.2016.02.002 · doi:10.1016/j.jaci.2017.02.007 · doi:10.1111/j.1398-9995.2011.02783.x · doi:10.3389/fcimb.2021.650893 · doi:10.1111/cei.13398

  4. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A broad body of reviews and mechanistic work documents that gut microbiota communicate with barrier tissues — including the skin — through microbial metabolites such as short-chain fatty acids, immune-cell trafficking, and systemic inflammatory signalling, establishing the gut microbiome as a biologically grounded lens for understanding skin health and disease.

    doi:10.1128/cmr.00270-24 · doi:10.1007/s00403-025-04285-w · doi:10.1097/j.pain.0000000000003376 · doi:10.1186/s41232-024-00334-5 · doi:10.1111/febs.16888 · doi:10.3390/ijms24119702

  5. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A broad and growing body of narrative reviews and observational research documents that gut microbial composition, diversity, and metabolite output — particularly short-chain fatty acids and tryptophan derivatives — are consistently altered across a wide range of inflammatory skin and systemic immune-mediated diseases, with proposed mechanisms including intestinal barrier disruption, microbial translocation, molecular mimicry, and dysregulated immune-cell polarisation.

    doi:10.34133/research.1097 · doi:10.3390/ijms262311652 · doi:10.1093/ibd/izaf228 · doi:10.3389/fmicb.2025.1644758 · doi:10.1002/acr.25623 · doi:10.3390/ijms26136076 · doi:10.3390/jpm15060237 · doi:10.3390/nu17091603 · doi:10.1007/s13555-023-00904-4 · doi:10.1016/j.biopha.2021.111904 · doi:10.4078/jrd.2021.28.2.55 · doi:10.14309/ajg.0000000000000305 · doi:10.1186/s13075-019-1872-4 · doi:10.1097/BOR.0000000000000569 · doi:10.3389/fmicb.2018.00432 · doi:10.3389/fmicb.2016.01081

  6. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A large and rapidly growing body of reviews, systematic analyses, and intervention studies documents consistent associations between gut microbiota composition and inflammatory skin disease, with mechanistic evidence pointing to microbial metabolites — particularly short-chain fatty acids and tryptophan derivatives — as candidate mediators that regulate intestinal barrier integrity, systemic immune tone, and distant skin inflammation through the gut-skin axis.

    doi:10.1007/s11882-026-01281-6 · doi:10.3390/antiox15030299 · doi:10.1080/19490976.2025.2574934 · doi:10.2147/IJGM.S550152 · doi:10.3389/fimmu.2025.1649857 · doi:10.3389/fmicb.2025.1613315 · doi:10.1080/19490976.2024.2430420 · doi:10.3389/fmicb.2024.1400657 · doi:10.1016/j.jid.2023.10.016

  7. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A large and growing body of reviews, systematic analyses, and clinical studies documents consistent gut microbiome alterations — reduced diversity, depletion of short-chain fatty acid-producing taxa, and disrupted metabolite signalling — across multiple chronic inflammatory skin diseases, while a grade-A systematic review and a grade-A randomised trial provide stronger evidence that these gut-skin microbial relationships are functionally relevant and therapeutically modifiable, establishing the gut microbiome as a biologically grounded lens on skin health.

    doi:10.1111/exd.70234 · doi:10.1128/msystems.01201-24 · doi:10.1128/spectrum.01154-23 · doi:10.1111/bjd.17931 · doi:10.3390/cells15070594 · doi:10.3389/fimmu.2026.1714515 · doi:10.1080/19490976.2025.2473524

  8. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A converging body of reviews and prospective cohort studies demonstrates that the gut microbiome is established through coordinated maternal-to-infant transmission across multiple routes — delivery mode, breast milk, and early skin contact — and that disruptions to this succession, whether from preterm birth, caesarean delivery, or antibiotic exposure, produce measurable shifts in microbial community structure that are associated with altered immune development and downstream health trajectories.

    doi:10.1080/19490976.2026.2673888 · doi:10.3389/frmbi.2025.1548650 · doi:10.1097/MCO.0000000000001209 · doi:10.1016/j.jri.2025.104542 · doi:10.1111/febs.70031 · doi:10.1128/spectrum.01636-24 · doi:10.1016/j.chom.2024.07.010 · doi:10.1111/aogs.14773 · doi:10.1080/19490976.2023.2295403 · doi:10.1080/19490976.2022.2038855 · doi:10.3390/microorganisms9102122 · doi:10.1590/1518.8345.4466.3446 · doi:10.3389/fimmu.2021.683022 · doi:10.3390/microorganisms8121855 · doi:10.1001/jamanetworkopen.2020.18119 · doi:10.3389/fimmu.2019.02939

  9. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A large and growing body of evidence — spanning systematic reviews, randomised controlled trials, and mechanistic research — documents consistent differences in gut microbial diversity and composition between individuals who develop inflammatory skin disease and those who do not, with short-chain fatty acids, tryptophan metabolites, and gut-educated immune cells proposed as candidate mediators linking intestinal ecology to cutaneous immune tone.

    doi:10.1007/s11882-026-01272-7 · doi:10.34763/jmotherandchild.20263001.d-25-00037 · doi:10.3390/ijms27010365 · doi:10.1186/s40001-025-03685-y · doi:10.1093/bjd/ljaf414 · doi:10.1016/j.tjnut.2025.10.006 · doi:10.3389/fmicb.2025.1549895 · doi:10.1159/000540075 · doi:10.1080/02770903.2024.2332921 · doi:10.3389/fimmu.2021.720393 · doi:10.1016/j.jaci.2018.09.025 · doi:10.2340/00015555-3008 · doi:10.1111/all.12700 · doi:10.3389/fped.2025.1498965

  10. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A broad body of reviews and mechanistic studies establishes the gut microbiome as a system-level regulator of skin biology, documenting that microbial metabolites — especially short-chain fatty acids produced by anaerobic fermenters — modulate immune tone, epithelial barrier integrity, and inflammatory signalling through the gut-skin axis. Multiple lines of evidence further show that gut dysbiosis, triggered by diet, environmental exposures, circadian disruption, or modern hygiene practices, propagates systemic inflammation that reaches the skin, while controlled interventions demonstrate

    doi:10.1093/femsle/fnag036 · doi:10.1007/s00248-026-02747-w · doi:10.3390/ijms27062521 · doi:10.1016/j.foodres.2026.118945 · doi:10.1186/s13062-026-00748-w · doi:10.3389/fimmu.2026.1738273 · doi:10.1186/s12967-025-07300-w · doi:10.4014/jmb.2511.11046 · doi:10.3390/pharmaceutics17101246 · doi:10.31083/FBL26283 · doi:10.1002/imt2.270 · doi:10.1038/s41598-024-68235-8 · doi:10.7759/cureus.61846 · doi:10.1007/s13555-022-00759-1 · doi:10.1016/j.scitotenv.2021.151654 · doi:10.1126/sciadv.aba2578

  11. 01

    Gut / Microbiome

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A convergent body of reviews, systematic analyses, and interventional trials links gut microbiome composition — particularly the balance between short-chain fatty acid-producing bacteria and pro-inflammatory taxa — to systemic immune tone and skin biology across multiple inflammatory dermatoses, supporting the gut microbiome as a biologically grounded lens on dermatology.

    doi:10.1111/exd.70261 · doi:10.3390/microorganisms14010063 · doi:10.3390/medicina61122090 · doi:10.3390/pathogens14111140 · doi:10.3390/microorganisms13112416 · doi:10.1007/s12602-025-10799-6 · doi:10.3390/biomedicines13082014 · doi:10.3389/fimmu.2025.1605434 · doi:10.3389/fphys.2025.1556998 · doi:10.1111/all.16372 · doi:10.1080/19490976.2024.2382774 · doi:10.3390/md21070379 · doi:10.3748/wjg.v22.i23.5415 · doi:10.3390/jcm14010019

  12. 07

    Skin Barrier

    Grade B : Solid — cohort / observational human

    The epidermal barrier is a biologically active interface whose structural proteins, lipid lamellae, redox-sensing pathways, and nuclear receptor networks collectively regulate keratinocyte differentiation, transepidermal water loss, antimicrobial defence, and systemic inflammatory tone — establishing skin-barrier integrity as a well-supported mechanistic lens for understanding a broad range of inflammatory, aging-related, and metabolic skin conditions.

    doi:10.3390/nu18091444 · doi:10.3389/fimmu.2026.1739412 · doi:10.3389/falgy.2026.1780908 · doi:10.1002/biof.70013 · doi:10.1016/j.jid.2024.09.025 · doi:10.3390/biom14060728 · doi:10.1111/exd.15107 · doi:10.3390/biology12111396 · doi:10.1111/1753-0407.13303 · doi:10.3390/antiox11071397 · doi:10.1016/j.freeradbiomed.2022.06.238 · doi:10.18632/aging.102946 · doi:10.1039/c8fo00843d · doi:10.3390/nu9121371 · doi:10.1016/j.jid.2017.01.007 · doi:10.3390/antiox9080751

  13. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A large and growing body of controlled clinical evidence — spanning randomised trials of emollients, ceramide-based formulations, and topical actives across dry, sensitive, aged, and procedure-stressed skin — consistently shows that stratum corneum hydration, transepidermal water loss, lipid composition, and pH together govern whether the skin retains water, resists irritants, and maintains immune homeostasis, establishing the skin barrier as a biologically and clinically grounded lens on dermatology.

    doi:10.1111/jocd.70898 · doi:10.36290/csf.2026.002 · doi:10.7759/cureus.100886 · doi:10.1111/jocd.70711 · doi:10.1159/000550716 · doi:10.1111/ijd.70081 · doi:10.1111/exd.70183 · doi:10.3390/pharmaceutics17111361 · doi:10.1002/clt2.70105 · doi:10.1159/000549265 · doi:10.1093/bjd/ljaf200 · doi:10.1111/ijd.17790 · doi:10.1080/09546634.2025.2486702 · doi:10.1111/jocd.70109 · pmid:40078856 · doi:10.1016/j.jid.2025.02.129 · doi:10.1111/jocd.16655 · doi:10.1016/j.jid.2024.07.009 · doi:10.5021/ad.23.078 · doi:10.1159/000534136 · doi:10.1371/journal.pone.0261253

  14. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A large and mechanistically diverse body of work—spanning proteolytic cascades that govern desquamation, structural proteins of the cornified envelope, keratinocyte-immune crosstalk, and post-translational modifications such as citrullination and S-palmitoylation—establishes the epidermal barrier as a biologically coherent and evidence-grounded lens on skin health, with disruption of its integrity recognized as a convergent driver across multiple inflammatory, inherited, and immunological skin conditions.

    doi:10.3390/dermatopathology13020022 · doi:10.1007/s00011-026-02186-w · doi:10.1007/s00441-026-04052-x · doi:10.1093/bjd/ljag068 · doi:10.3390/biom16010053 · doi:10.2147/JIR.S558464 · doi:10.3390/biom15070913 · doi:10.1016/j.molmed.2025.03.012 · doi:10.3389/fimmu.2025.1510559 · doi:10.3390/ijms26041673 · doi:10.3389/fimmu.2024.1448952 · doi:10.3389/fimmu.2023.1239598 · doi:10.1098/rstb.2022.0245 · doi:10.3389/fimmu.2023.1111611 · doi:10.3390/ijms232314962 · doi:10.3389/fimmu.2022.1003970 · doi:10.1016/j.jdermsci.2022.06.004 · doi:10.3390/cells11132026 · doi:10.1152/ajpcell.00052.2022 · doi:10.3389/fmed.2021.777619 · doi:10.1002/path.5888 · doi:10.3389/fimmu.2021.808012 · doi:10.3389/fimmu.2021.646316 · doi:10.1111/exd.14470 · doi:10.3389/fimmu.2021.695373 · doi:10.3390/ijms22115575 · doi:10.3389/fmed.2021.665647 · doi:10.3390/ijms22094677 · doi:10.1007/s00204-021-03042-y · doi:10.1080/10408363.2020.1775171 · doi:10.1016/j.jid.2020.05.095 · doi:10.1111/exd.14104 · doi:10.1016/j.ab.2020.113606 · doi:10.3390/ijms21020566 · doi:10.1038/s41598-019-53874-z · doi:10.1007/s12192-019-01044-5 · doi:10.3390/cells8080807 · doi:10.1016/j.jdermsci.2019.06.007 · doi:10.1111/exd.13936 · doi:10.18926/AMO/56452 · doi:10.1126/scitranslmed.aat2004 · doi:10.1111/jdv.15301 · doi:10.1111/exd.13449 · doi:10.1111/exd.13317 · doi:10.1016/j.tibs.2009.08.001 · doi:10.1083/jcb.200709098 · doi:10.1007/s00018-005-5196-y · doi:10.3389/fimmu.2025.1694066 · doi:10.1111/exd.70181 · doi:10.3390/diagnostics13203167 · doi:10.1080/14789450.2021.2003707 · doi:10.3389/fcell.2021.621318 · doi:10.17179/excli2020-3114 · doi:10.1172/jci.insight.142067 · pmid:32226343 · doi:10.1155/2018/5404093 · doi:10.1038/jid.2015.58 · doi:10.1093/molbev/msu251 · doi:10.1074/jbc.M112.357467 · doi:10.3349/ymj.2010.51.6.808

  15. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    The stratum corneum's lipid-protein architecture acts as the skin's primary rate-limiting barrier, and a growing body of preclinical and formulation science demonstrates that disruptions to this barrier — whether genetic, inflammatory, or disease-driven — alter drug penetration, immune activation, and tissue hydration in biologically meaningful ways, establishing skin-barrier integrity as a well-grounded mechanistic lens for understanding and treating diverse dermatological conditions.

    doi:10.1007/s13205-026-04877-x · doi:10.1080/09205063.2026.2675319 · doi:10.3389/fbioe.2026.1797044 · doi:10.1016/j.ijbiomac.2026.151021 · doi:10.1007/s13659-025-00585-w · doi:10.1016/j.ijpharm.2026.126603 · doi:10.3390/molecules30234493 · doi:10.1016/j.bcp.2025.117567 · doi:10.7759/cureus.94120 · doi:10.1016/j.ijpharm.2025.126306 · doi:10.3390/pharmaceutics17101281 · doi:10.1111/jocd.70514 · doi:10.1186/s12951-025-03660-z · doi:10.1080/09205063.2025.2535492 · doi:10.3389/fphar.2025.1607210 · doi:10.3390/pharmaceutics17060746 · doi:10.1080/17435889.2025.2506347 · doi:10.1080/17435889.2025.2492538 · doi:10.1007/s13346-025-01809-9 · doi:10.1016/j.xjidi.2024.100340 · doi:10.3390/pharmaceutics16121561 · doi:10.2174/0122117385345369241212071947 · doi:10.1016/S1875-5364(24)60681-3 · doi:10.1016/j.carbpol.2024.122966 · doi:10.3390/pharmaceutics16111403 · doi:10.3390/pharmaceutics16111384 · doi:10.1007/s40290-024-00537-8 · doi:10.1016/j.ejpb.2024.114474 · doi:10.1080/17435889.2024.2375193 · doi:10.1016/j.ijpharm.2024.124435 · doi:10.1016/j.ejpb.2024.114394 · doi:10.3390/ijms25105375 · doi:10.1021/acs.molpharmaceut.4c00144 · doi:10.3389/fimmu.2024.1361005 · doi:10.1080/02652048.2024.2326085 · doi:10.1208/s12249-023-02649-x · doi:10.4155/tde-2023-0033 · doi:10.1007/s43440-023-00510-3 · doi:10.1080/10837450.2023.2251556 · doi:10.3390/pharmaceutics15082165 · doi:10.3390/pharmaceutics15020657 · doi:10.1248/yakushi.22-00113 · doi:10.3349/ymj.2022.0092 · pmid:36053767 · doi:10.1208/s12249-022-02344-3 · doi:10.1016/j.ijpharm.2022.121656 · doi:10.1016/j.biopha.2022.112633 · doi:10.1016/j.ijpharm.2021.121447 · doi:10.3390/cells10113096 · doi:10.1002/anie.202107960 · doi:10.1111/ijd.15733 · doi:10.1016/j.ejpb.2021.07.006 · doi:10.3390/ijms22116078 · doi:10.2174/1381612827666210526091825 · doi:10.1111/jocd.14037 · doi:10.1080/10717544.2021.1889717 · doi:10.3390/pharmaceutics12121224 · doi:10.1016/j.ejps.2020.105638 · doi:10.3389/fphar.2020.01105 · doi:10.2174/1872211314999200819152450 · doi:10.2174/1567201817666200804105416 · doi:10.1007/s13346-020-00823-3 · doi:10.1002/adma.202002129 · doi:10.1021/acs.molpharmaceut.0c00154 · doi:10.1016/j.ijpharm.2020.119031 · doi:10.2174/1381612826666200114090659 · doi:10.3390/ijms20225659 · doi:10.1007/s40257-019-00480-4 · doi:10.2174/1567201816666190201143457 · doi:10.1007/s00105-018-4343-y · doi:10.1208/s12249-018-1196-8 · doi:10.1016/j.ijpharm.2018.10.027 · doi:10.1016/j.ijpharm.2018.09.046 · doi:10.2147/IJN.S170745 · doi:10.1016/j.ijpharm.2018.08.007 · doi:10.15171/apb.2018.021 · doi:10.1016/j.ijpharm.2018.06.012 · doi:10.1007/s00403-018-1841-9 · doi:10.1016/j.ijpharm.2018.04.057 · doi:10.1002/tcr.201700061 · doi:10.2174/1566523217666170510151540 · doi:10.3389/fphar.2023.1333986 · doi:10.1007/s13346-023-01307-w · doi:10.1016/j.heliyon.2022.e08938 · doi:10.1007/s00420-009-0405-x

  16. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    Skin barrier dysfunction — driven by genetic variants in structural proteins such as filaggrin, disrupted lipid composition, and cytokine-mediated suppression of terminal keratinocyte differentiation — is a foundational and well-characterised mechanism through which the epidermis loses its protective integrity, permitting allergen and microbial penetration that amplifies systemic immune dysregulation.

    doi:10.3389/fimmu.2026.1788831 · doi:10.1016/j.jaad.2025.04.027 · doi:10.1016/j.jaci.2024.09.017 · doi:10.1016/j.jaci.2023.12.027 · doi:10.1111/jdv.19081 · doi:10.1016/j.jaci.2018.08.022

  17. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A large body of research documents that the skin's physical and microbial barrier functions are deeply interdependent: structural proteins such as filaggrin, stratum corneum lipids, skin pH, and the resident microbial community collectively regulate epidermal permeability and innate immune tone, with disruption of any one component amplifying dysfunction in the others.

    doi:10.3390/ijms262311737 · doi:10.1080/13543784.2024.2326625 · doi:10.1016/j.jaad.2022.11.047 · doi:10.3390/ijms22168403 · doi:10.1111/all.14461 · doi:10.1002/ctm2.790 · doi:10.3389/fcimb.2021.720674 · doi:10.1016/j.jid.2019.05.024

  18. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A large and heterogeneous body of evidence — spanning randomised controlled trials of oral lipids, ceramides, and hyaluronic acid through to mechanistic work on stratum corneum lipid transport and natural moisturising factor synthesis — consistently shows that nutritional and topical inputs can modulate the physical integrity of the epidermal barrier, as measured by transepidermal water loss, stratum corneum hydration, and structural protein expression, establishing skin-barrier biology as a biologically grounded and clinically tractable lens on skin health across diverse conditions and

    doi:10.1038/s41598-025-34887-3 · doi:10.1038/s41598-025-32758-5 · doi:10.3390/ijms26010246 · doi:10.1016/j.lfs.2024.123149 · doi:10.1111/jocd.16513 · doi:10.3390/nu16132100 · doi:10.1111/srt.13666 · doi:10.1111/jocd.16130 · doi:10.1111/srt.13202 · doi:10.3390/nu14132737 · doi:10.1159/000520009 · doi:10.1024/0300-9831/a000699 · doi:10.5650/jos.ess20115 · doi:10.1007/s13668-020-00322-4 · doi:10.1111/1346-8138.15428 · doi:10.1111/ics.12612 · doi:10.1186/s12906-019-2721-3 · pmid:30681787 · doi:10.3177/jnsv.64.265 · doi:10.3390/nu10070817 · doi:10.1039/c7fo01548h · doi:10.1080/09168451.2017.1345614 · doi:10.6133/apjcn.052016.05 · doi:10.1016/j.ijpharm.2017.01.054

  19. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    The skin barrier — comprising the stratum corneum's lipid matrix, filaggrin-derived natural moisturising factors, and acid mantle — functions as the body's primary interface against water loss, microbial entry, and allergen penetration, with structural immaturity or genetic deficits in any of these components measurably elevating permeability and downstream immune activation across the lifespan.

    doi:10.7759/cureus.105971 · doi:10.7759/cureus.105137 · doi:10.1093/bjd/ljaf465.024 · doi:10.1111/pde.70010 · doi:10.1016/j.jaip.2025.03.046 · doi:10.4168/aair.2025.17.1.32 · doi:10.3310/RHDN9613 · doi:10.1093/bjd/ljae091 · doi:10.1111/cea.14381 · doi:10.1111/pai.13998 · doi:10.23736/S2784-8671.23.07336-X · doi:10.2340/actadv.v103.5671 · doi:10.1002/14651858.CD013534.pub3 · doi:10.1111/all.15491 · doi:10.1111/cod.14177 · doi:10.1016/j.anai.2022.02.012 · doi:10.3390/pharmaceutics14020433 · doi:10.36849/jdd.6219 · doi:10.1371/journal.pmed.1003680 · doi:10.1111/jdv.17675 · doi:10.1111/ajd.13703 · doi:10.7189/jogh.11.04047 · doi:10.1002/14651858.CD001150.pub4 · doi:10.1016/j.jaci.2020.10.044 · doi:10.1111/cea.13847 · doi:10.1002/14651858.CD013534.pub2 · doi:10.1097/01.ASW.0000672500.18525.2e · doi:10.7189/jogh.10.010414 · doi:10.1097/MD.0000000000020329 · doi:10.1111/pde.14169 · doi:10.1016/S0140-6736(19)32984-8 · doi:10.1186/s12887-019-1871-2 · doi:10.1111/pde.14037 · pmid:31584781 · doi:10.1159/000501636 · doi:10.1111/jdv.15786 · doi:10.3122/jabfm.2019.02.180225 · doi:10.1111/pde.13725 · doi:10.1111/pde.13714 · doi:10.1016/j.earlhumdev.2018.03.002 · doi:10.1038/jp.2017.158 · doi:10.1016/j.midw.2017.10.001 · doi:10.1111/1346-8138.14080 · doi:10.1111/ijd.13735 · doi:10.1186/s13063-017-2031-3 · doi:10.1111/jocd.12302 · doi:10.1016/j.jaci.2014.08.005 · doi:10.1111/1552-6909.12015 · doi:10.1186/1471-2431-12-59 · doi:10.1186/1471-5945-12-3

  20. 07

    Skin Barrier

    Grade C : Emerging — mechanistic / animal / in-vitro

    Genetic dissection of inherited cornification disorders — from SPINK5/LEKTI-mediated protease dysregulation and kallikrein cascades to mutations in structural keratins, ceramide-synthesis enzymes, and desmosomal proteins — consistently converges on a single downstream consequence: a disrupted stratum corneum that permits water loss, allergen penetration, and pathogen entry, while triggering compensatory inflammation.

    doi:10.1002/path.70018 · doi:10.34763/jmotherandchild.20252901.d-25-00014 · doi:10.1038/s41572-022-00412-3 · doi:10.3390/ijms222212446 · doi:10.2340/00015555-3432 · doi:10.2340/00015555-3433 · doi:10.12688/f1000research.14514.1 · doi:10.1007/s40257-017-0313-x

  21. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    Converging review evidence frames epithelial barrier dysfunction as a central, biologically grounded lens on inflammatory skin and mucosal disease: environmental exposures damage structural proteins and tight-junction complexes in the stratum corneum, triggering alarmin release, microbial dysbiosis, and type-2 immune cascades that propagate beyond the skin to multiple organ systems.

    doi:10.4168/aair.2023.15.6.705 · doi:10.1111/cod.13959 · doi:10.1016/j.jaci.2020.02.021 · doi:10.1172/JCI124608 · doi:10.4049/jimmunol.0901860 · doi:10.1111/all.16318 · doi:10.3389/fimmu.2024.1348272 · doi:10.1016/j.jaci.2017.04.010 · doi:10.1038/ajg.2015.247 · doi:10.1183/09059180.00004314

  22. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    The stratum corneum functions as the body's primary physical interface with the environment, regulating water retention, pathogen exclusion, and immune homeostasis through a tightly organised matrix of corneocytes, intercellular lipids, and structural proteins; disruption of this layer — measurable via transepidermal water loss, Raman spectroscopy, impedance, and related biophysical tools — is consistently linked to impaired skin integrity across a broad range of inflammatory and wound-healing contexts, establishing the skin barrier as a foundational, evidence-supported lens for understanding

    pmid:41804153 · doi:10.1089/wound.2024.0148 · doi:10.2337/dc25-0300 · doi:10.1111/exd.14635 · doi:10.1002/ski2.104 · doi:10.3390/molecules26061649 · doi:10.3390/pharmaceutics12070684 · doi:10.1111/exd.14055 · doi:10.1016/j.jid.2018.09.001 · doi:10.1111/exd.13743

  23. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    Converging epidemiological, mechanistic, and interventional evidence shows that environmental pollutants — including particulate matter, gaseous oxidants, synthetic chemicals, and climate-driven temperature extremes — disrupt skin-barrier proteins such as filaggrin, deplete cutaneous antioxidants, and activate inflammatory signalling cascades, establishing the skin barrier as a biologically grounded and clinically relevant lens for understanding how environmental exposures translate into inflammatory skin disease.

    doi:10.1111/jocd.70306 · doi:10.1111/exd.70069 · doi:10.1186/s12989-020-00366-y · doi:10.1007/s00105-018-4330-3 · pmid:30235385

  24. 07

    Skin Barrier

    Grade B : Solid — cohort / observational human

    The skin barrier is maintained by a tightly regulated programme of keratinocyte proliferation, differentiation, and cornification — orchestrated by transcription factors such as p63, epigenetic remodelling complexes, and structural proteins including filaggrin and keratins — whose disruption underlies a broad spectrum of inherited and acquired skin diseases. Epidermal stem cells drive continuous self-renewal and injury repair, while the extracellular matrix, integrin signalling, and matricellular proteins coordinate the microenvironmental cues that sustain barrier integrity across the

    doi:10.3390/ijms25010236 · doi:10.3390/ijms23094874 · doi:10.1111/vde.12956 · doi:10.1111/exd.14305 · doi:10.1016/j.jid.2020.09.007 · doi:10.1111/exd.13696 · doi:10.1007/s00018-017-2701-z · doi:10.1007/s00018-008-8119-x

  25. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A substantial body of genetic evidence — spanning landmark meta-analyses, systematic reviews, and longitudinal cohort studies — establishes loss-of-function mutations in the filaggrin gene as a major determinant of skin-barrier integrity, with downstream consequences for allergic sensitisation, respiratory disease, and food allergy across populations worldwide.

    doi:10.1111/pai.70326 · doi:10.1111/exd.15130 · doi:10.1136/bmj.b2433 · doi:10.1016/j.jaci.2009.03.036 · doi:10.1038/s41598-020-59627-7 · doi:10.1111/bjd.18778 · doi:10.1371/journal.pone.0099437

  26. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    Converging genetic, genomic, and biomarker evidence establishes the skin barrier as a biologically grounded lens on skin health: loss-of-function variants in structural proteins such as filaggrin and SPINK5 show strong, replicated associations with inflammatory skin disease across diverse populations, large-scale GWAS analyses implicate over 100 loci linked to epidermal differentiation and barrier integrity, and prospective birth-cohort work demonstrates that measurable barrier disruption—detectable before clinical disease onset—predicts downstream immune sensitization and systemic allergic

    doi:10.1590/1984-0462/2025/43/2025111 · doi:10.1038/s41467-025-58310-7 · doi:10.1016/j.jaci.2024.02.018 · doi:10.1111/jdv.19932 · doi:10.1007/s00431-022-04436-5 · doi:10.1016/j.jaip.2019.10.007 · doi:10.1111/cea.13156 · doi:10.1097/MD.0000000000021256 · doi:10.1093/hmg/ddt317

  27. 07

    Skin Barrier

    Grade B : Solid — cohort / observational human

    Filaggrin, a structural protein of the outermost epidermal layer, orchestrates keratin filament organisation, corneocyte formation, and the generation of natural moisturising factors that sustain hydration and surface acidity; decades of biochemical, genetic, and mechanistic research establish that loss or dysfunction of this protein disrupts skin barrier integrity across a spectrum of heritable and acquired skin conditions.

    doi:10.1111/cup.14756 · doi:10.1111/ics.12974 · doi:10.1016/j.jbc.2024.107634 · doi:10.3390/ijms23031455 · doi:10.1007/s12272-021-01305-x · doi:10.1016/j.anai.2019.10.008 · doi:10.11613/BM.2019.020501 · doi:10.3390/cells8050489 · doi:10.1038/jid.2011.393 · doi:10.1016/j.jaci.2014.06.014 · doi:10.1016/j.jaci.2012.12.668 · doi:10.1128/mcb.13.1.613-625.1993 · doi:10.1021/bi00089a020 · doi:10.1242/jcs.106.1.219 · doi:10.1021/bi00029a024 · doi:10.1074/jbc.270.47.28193 · doi:10.1016/0167-4838(83)90336-9 · doi:10.1021/bi00266a033 · doi:10.1016/0012-1606(86)90230-7 · pmid:2298727 · pmid:1429717 · doi:10.1111/bjd.14997

  28. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    Converging genetic, epidemiological, and mechanistic evidence establishes skin-barrier integrity as a biologically grounded lens on inflammatory and allergic skin disease: loss-of-function variants in barrier genes increase transepidermal water loss and facilitate percutaneous allergen sensitization, a large meta-analysis identifies elevated transepidermal water loss as among the strongest predictors of allergic sensitization in early life, and real-time monitoring of skin permeability during allergen challenge has demonstrated prospective utility as a physiological biomarker—collectively

    doi:10.1001/jamapediatrics.2025.6105 · doi:10.1001/jamanetworkopen.2025.43371 · doi:10.1007/s11882-025-01218-5 · doi:10.3390/nu15051070

  29. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    Ceramides — a structurally diverse family of sphingolipids that constitute roughly half of the lipid matrix of the stratum corneum — are essential architects of the skin's permeability barrier, working alongside cholesterol and free fatty acids to form the ordered lamellar structures that limit water loss and restrict penetration of external agents. Evidence from human clinical trials, randomised controlled studies, genetic models, and lipidomic analyses consistently links the composition, chain-length distribution, and subclass balance of ceramides to barrier integrity across a range of

    doi:10.1111/jocd.70795 · doi:10.1016/j.jsbmb.2025.106842 · doi:10.1111/exd.70042 · doi:10.4168/aair.2024.16.5.445 · doi:10.1111/ics.12972 · doi:10.1016/j.jlr.2024.100591 · doi:10.3390/pharmaceutics16060807 · doi:10.1016/j.pharmthera.2024.108681 · doi:10.1159/000535049 · doi:10.1016/j.plipres.2023.101264 · doi:10.1016/j.plipres.2023.101252 · doi:10.1016/j.jdermsci.2023.02.007 · doi:10.3892/ijmm.2023.5229 · doi:10.1097/MCO.0000000000000902 · doi:10.1016/j.jid.2022.07.029 · doi:10.3390/ijms23179697 · doi:10.1016/j.plipres.2022.101184 · doi:10.1021/acs.jafc.2c01731 · doi:10.3390/metabo12080685 · doi:10.3390/biology11060809 · doi:10.3390/nano12020275 · doi:10.5650/jos.ess21128 · doi:10.3389/fmicb.2021.690211 · doi:10.1007/s40257-021-00619-2 · doi:10.3390/ijms22105229 · doi:10.1016/j.addr.2021.05.012 · doi:10.36849/JDD.2021.589c · doi:10.36849/JDD.2021.589b · doi:10.36849/JDD.2021.589a · doi:10.1159/000513261 · doi:10.1016/j.jdermsci.2020.10.003 · doi:10.1159/000509019 · doi:10.1016/j.heliyon.2020.e03955 · doi:10.1111/exd.14106 · doi:10.1194/jlr.RA120000671 · doi:10.1371/journal.pgen.1008628 · doi:10.1016/j.jdermsci.2019.12.002 · doi:10.1248/yakushi.19-00181-1 · doi:10.1208/s12249-019-1497-6 · doi:10.1016/j.lfs.2018.12.040 · doi:10.1186/s41232-018-0089-2 · doi:10.1016/j.jid.2018.10.034 · doi:10.1016/j.chemphyslip.2018.09.017 · doi:10.1016/j.bbalip.2018.09.010 · doi:10.1159/000489530 · doi:10.3390/ijms19010247 · doi:10.1042/BST20160469 · doi:10.2340/00015555-2865 · doi:10.1248/yakushi.17-00126 · doi:10.1016/j.jdermsci.2017.06.002 · doi:10.1159/000464337 · doi:10.1111/ics.12399 · doi:10.1021/acsomega.4c11687 · doi:10.3390/ijms24021456 · doi:10.3389/fphys.2021.804824 · doi:10.3390/jcm9030736 · doi:10.1111/ics.12038

  30. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A growing body of research applies genomic, transcriptomic, proteomic, lipidomic, and metabolomic tools to the skin barrier, collectively mapping how structural proteins, lipid composition, and surface chemistry interact to maintain epidermal integrity and regulate immune tone across a range of inflammatory dermatoses. Non-invasive sampling methods — including tape stripping, skin blotting, and surface lipid collection — have enabled molecular profiling of the stratum corneum in living subjects, validating the skin barrier as a measurable, biologically tractable lens on dermatological health.

    doi:10.1038/s41598-025-23579-7 · doi:10.3390/microorganisms13081771 · doi:10.1093/bjd/ljaf275 · doi:10.1016/j.jid.2025.05.013 · doi:10.1111/exd.70018 · doi:10.1016/j.jid.2024.09.003 · doi:10.1002/prca.202300106 · doi:10.3390/cimb45060331 · doi:10.2174/1573396320666230411093122 · doi:10.7150/ijms.73150 · doi:10.1111/wrr.13030 · doi:10.1159/000514308 · doi:10.1111/exd.14276 · doi:10.1111/bjd.19760 · doi:10.1038/s41598-020-78943-6 · doi:10.1016/j.jdermsci.2020.10.011 · doi:10.1016/j.jaci.2020.06.015 · doi:10.1016/j.jaci.2020.06.012 · doi:10.1016/j.jaci.2020.04.022 · doi:10.1111/jocd.13188 · doi:10.1016/j.jid.2019.03.1160 · doi:10.12788/j.sder.2019.004 · doi:10.1016/j.jid.2017.08.036 · doi:10.1016/j.jid.2017.05.040 · doi:10.1016/j.jaci.2010.10.033 · doi:10.3389/fimmu.2024.1401102 · doi:10.3390/ijms25021042 · doi:10.3390/ijms23158791 · doi:10.1016/j.jaci.2017.10.046 · doi:10.1155/2010/364823

  31. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    The skin barrier — spanning the stratum corneum lipid matrix, tight junctions, antimicrobial defenses, and immune sentinels — functions as the primary interface between internal physiology and the external environment, and its structural or functional compromise has been documented across a wide range of inflammatory, occupational, metabolic, and iatrogenic skin diseases.

    doi:10.1684/ejd.2026.5032 · doi:10.1007/s00280-025-04842-0 · doi:10.1111/cod.14808 · doi:10.1111/all.16466 · doi:10.1111/cod.14532 · doi:10.1111/jocd.16226 · doi:10.1111/ics.12926 · doi:10.1111/cod.14287 · doi:10.1530/EJE-21-1197 · doi:10.1111/cod.14034 · doi:10.1111/ddg.14359 · doi:10.1097/DER.0000000000000612 · doi:10.1111/cod.13502 · doi:10.1111/jdv.16288 · doi:10.1684/ejd.2018.3352

  32. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    The skin barrier is a multilayered physicochemical and immunological system — spanning the stratum corneum lipid matrix, structural proteins such as filaggrin, tight junctions, antimicrobial peptides, and the resident microbiome — whose integrity is fundamental to skin homeostasis across a broad range of inflammatory and degenerative conditions. Convergent evidence from clinical trials, controlled topical interventions, genetic association studies, and mechanistic in-vitro and in-vivo work demonstrates that barrier disruption is both a cause and consequence of cutaneous inflammation, with

    doi:10.2147/IJN.S598256 · doi:10.3390/nu18091365 · doi:10.1016/j.cbi.2026.112066 · doi:10.3390/ijms262411855 · doi:10.1111/1346-8138.17975 · doi:10.1186/s13287-025-04649-z · doi:10.2478/acph-2024-0014 · doi:10.3390/ijms241612979 · doi:10.3390/cells10113176 · doi:10.1016/j.jid.2020.09.029 · doi:10.3390/ijms21207607 · doi:10.1111/jcmm.15208 · doi:10.1016/j.jaci.2019.06.047 · doi:10.1111/ced.13841 · doi:10.1016/j.anai.2018.03.013 · doi:10.18632/aging.101326 · doi:10.1016/j.jdermsci.2017.09.002 · doi:10.1016/j.jdermsci.2017.05.015 · doi:10.1056/NEJMoa021481

  33. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    Converging evidence from genetics, molecular biology, and immunology establishes the skin barrier as a foundational lens on inflammatory skin disease: loss-of-function variants in structural proteins such as filaggrin impair the stratum corneum, elevate transepidermal water loss, and permit allergen and microbial penetration, which in turn triggers keratinocyte alarmin release and downstream immune polarisation.

    doi:10.3389/falgy.2026.1798037 · doi:10.2147/JIR.S578036 · doi:10.1016/j.anai.2025.11.005 · doi:10.3389/fimmu.2025.1645095 · doi:10.3390/ijms262010162 · doi:10.3389/falgy.2025.1668742 · doi:10.3390/ijms26199623 · doi:10.1159/000548517 · doi:10.3389/fimmu.2025.1628163 · doi:10.3390/jcm14165633 · doi:10.1007/s10787-025-01900-0 · doi:10.1016/j.abd.2025.501136 · doi:10.14789/ejmj.JMJ24-0036-R · doi:10.3390/cells13161398 · doi:10.3389/fmed.2024.1342176 · doi:10.1007/s13555-023-01081-0 · doi:10.1016/j.cell.2023.10.019 · doi:10.1016/j.jaci.2023.05.004 · doi:10.3389/fmed.2023.1165098 · doi:10.3390/jcm11195633 · doi:10.3389/fimmu.2022.943640 · doi:10.1093/hmg/ddab342 · doi:10.1016/j.jdermsci.2021.01.005 · doi:10.1016/j.jdermsci.2020.12.004 · doi:10.3390/jcm9113741 · doi:10.1111/1346-8138.15664 · doi:10.3390/ijms21155382 · doi:10.1248/bpb.b19-00088 · doi:10.1111/imm.13120 · doi:10.3390/ijms20174234 · doi:10.1016/j.it.2018.10.001 · doi:10.1186/s41232-017-0044-7 · doi:10.1111/imr.12545

  34. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    Converging genetic, lipidomic, and mechanistic evidence establishes the stratum corneum as a structurally active barrier whose integrity depends on a precisely orchestrated programme of protein expression, ceramide biosynthesis, and lipid lamellar organisation; disruption of any of these components — whether through loss-of-function variants, altered lipid enzyme activity, or cytokine-driven downregulation of structural proteins — reproducibly increases epidermal permeability, elevates transepidermal water loss, and primes the skin for immune dysregulation across multiple inflammatory

    doi:10.1016/j.jid.2024.02.010 · doi:10.3390/cells12242793 · doi:10.1111/bjd.17896 · doi:10.1111/bjd.16934 · doi:10.1016/j.jdermsci.2017.05.005 · doi:10.1016/j.jaci.2013.12.1079 · doi:10.1016/j.jaci.2009.09.031

  35. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A substantial body of randomised trials and mechanistic reviews demonstrates that the skin barrier — defined by stratum corneum lipid architecture, structural proteins such as filaggrin, and transepidermal water loss — is a biologically tractable system whose integrity can be measured, perturbed, and restored through topical interventions, making it a well-evidenced lens on inflammatory and dry-skin biology.

    doi:10.1111/1346-8138.70117 · doi:10.2147/IJGM.S542311 · doi:10.1038/s41598-025-18487-9 · doi:10.1016/j.ecoenv.2025.118545 · doi:10.1159/000545433 · doi:10.1111/jocd.70051 · doi:10.36849/JDD.2024.7958 · doi:10.1111/jdv.20258 · doi:10.36849/JDD.8641 · doi:10.1007/s00403-023-02723-1 · doi:10.1111/srt.13475 · doi:10.1111/pde.15355 · doi:10.1111/jdv.18949 · doi:10.1111/jdv.18947 · doi:10.2147/CCID.S389697 · doi:10.1007/s00403-022-02400-9 · doi:10.1016/j.anai.2022.01.012 · doi:10.1111/1346-8138.16160 · doi:10.1159/000513055 · doi:10.1111/cea.13797 · doi:10.1097/DER.0000000000000623 · doi:10.1007/s40257-020-00529-9 · pmid:32484623 · doi:10.1016/j.abd.2019.11.007 · doi:10.2340/00015555-3296 · doi:10.1097/DER.0000000000000459 · doi:10.1186/s12895-019-0082-8 · doi:10.1159/000493641 · doi:10.1371/journal.pone.0192443 · doi:10.23736/S0392-0488.18.05898-4 · doi:10.1002/14651858.CD012119.pub2 · doi:10.1016/j.jaci.2009.07.015 · doi:10.1111/pde.12786

  36. 07

    Skin Barrier

    Grade B : Solid — cohort / observational human

    The skin barrier is a multilayered biological system — spanning the stratum corneum's lipid-protein architecture, tight junctions, the dermoepidermal junction, and resident immune cells — whose coordinated function prevents water loss, blocks pathogen entry, and regulates immune signalling; genetic studies, developmental data, and mechanistic work across multiple inflammatory dermatoses converge to establish barrier integrity as a foundational lens on skin biology broadly.

    doi:10.1016/j.cytogfr.2025.12.009 · doi:10.3390/cells14181438 · doi:10.7759/cureus.86937 · doi:10.1159/000546770 · doi:10.1146/annurev-immunol-082323-030832 · doi:10.1111/jdv.20463 · doi:10.3390/cells12232745 · doi:10.1016/j.mucimm.2023.02.005 · doi:10.3390/ijms24043145 · doi:10.1152/ajpcell.00069.2022 · doi:10.1002/ski2.99 · doi:10.3390/biom10121607 · doi:10.1038/s41390-020-1035-y · doi:10.3390/ijms21041194 · doi:10.1038/s41598-020-58718-9 · pmid:30681811 · doi:10.1111/j.1600-0625.2008.00786.x · doi:10.1111/j.1600-0625.2005.00363.x · doi:10.1038/nrm1619 · doi:10.3390/ijms222111676 · doi:10.1101/cshperspect.a018218 · doi:10.1172/JCI28521

  37. 07

    Skin Barrier

    Grade A : Strongest — systematic review / meta-analysis / RCT

    A converging body of evidence — from large-scale genome-wide association studies identifying filaggrin and keratin-pathway variants as major susceptibility loci, to mechanistic work showing that commensal microorganisms actively shape stratum corneum formation, pH homeostasis, and antimicrobial peptide expression — establishes skin-barrier integrity as a biologically grounded and clinically relevant lens on dermatology.

    doi:10.1038/s41467-026-69670-z · doi:10.2147/CCID.S574431 · doi:10.3390/ijms242115962 · doi:10.3390/ijms232113071 · doi:10.1126/science.abo0693

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