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LL-37 (Cathelicidin)
Alead outcome
Endogenous antimicrobial defense
grades vary by outcome ↓
Peptide
also called — LL-37 · cathelicidin (the human cathelicidin) · the C-terminal active fragment of hCAP18 (gene CAMP)
(defensive:) antimicrobialwound healingangiogenesis(pathological when dysregulated:) rosacea / psoriasis / lupus inflammation(gray-market pitch:) healing / anti-infective / skin
The double-edged sword of innate immunity — a natural antibiotic that, dysregulated, drives inflammatory disease. LL-37 is unusual in this register: it's sold as a healing/antimicrobial peptide, yet its largest and strongest evidence base is about its role in causing skin disease (rosacea, psoriasis, lupus). Three threads: (1) it's the body's own broad-spectrum antimicrobial peptide and a genuine innate-immune effector; (2) it has a "dual role" — antimicrobial and an "alarmin" that, when mis-processed or over-expressed, triggers inflammation, redness, and autoimmunity; (3) that means exogenous LL-37, marketed as healing, can plausibly feed the very inflammatory conditions its biology is famous for — the opposite of the intended pitch.
In brief
LL-37 is the body's own broad-spectrum antimicrobial peptide — the only human cathelicidin — a 37-amino-acid innate-immune effector made by skin and immune cells, switched on by vitamin D and injury, and activated by protease cleavage. It genuinely kills microbes (by disrupting their membranes) and supports wound healing and angiogenesis. But its defining feature is a dual role: it's also an "alarmin," and when its expression or processing goes wrong, it becomes a driver of inflammatory and autoimmune disease — it generates the inflammatory fragments of rosacea, breaks tolerance to self-DNA in psoriasis (via TLR9), and feeds lupus. That's the paradox for a register: LL-37 is sold as a healing/antimicrobial peptide, but its largest, most rigorous evidence base is about how it causes skin disease when dysregulated. As an exogenous therapeutic it's preclinical with no approvals, and administering a pro-inflammatory alarmin — particularly to anyone prone to rosacea or psoriasis — could plausibly do the opposite of healing. A fascinating, important molecule; a genuinely double-edged one; not a validated therapy.
Legal standing, by region
European Union
not an approved drug
not an approved drug; investigational. Not an approved cosmetic ingredient (an injectable pro-inflammatory alarmin is not a topical cosmetic). No compounding pathway.
An honest grade per outcome — drawn from the evidence, not any catalogue. Hype and undemonstrated marketing claims grade low.
OutcomeEvidence base · effectGrade
Endogenous antimicrobial defense
This grades LL-37's natural role — NOT a demonstrated benefit of taking exogenous LL-37
Extensive: potent broad-spectrum membrane-disrupting killing; surges in wounds
AExogenous wound healing / antimicrobial therapy (the marketed use)
No approved product; no human trials establishing efficacy or safety of exogenous use
Preclinical / early; angiogenic & pro-healing in models
DRole in rosacea (as a cause)
This is evidence it drives disease — a reason for caution, not a therapeutic credential
Strong: abnormal processing → pro-inflammatory fragments → erythema/telangiectasia
ARole in psoriasis / lupus (as a cause)
Again: robust evidence of harm/pathogenic role, underscoring the risk of exogenous use
Strong: LL-37+self-DNA→TLR9→break self-tolerance; T-cell autoantigen; NET/IFN in SLE
ASafety of exogenous administration
It's a pro-inflammatory alarmin; plausible to trigger/worsen inflammatory-autoimmune skin disease; contraindicated intuition for rosacea/psoriasis-prone users
Not established in humans
—Disclosure
Vallydia sells its own cosmetic serums, and some ingredients graded here belong to the same categories as those products. Grades are drawn from the published evidence by the method we publish, and applied to our own ingredients on the same terms — our copper-peptide serum is graded no more kindly than the peptides it competes with. We disclose the interest so you can weigh it.
Trade names shown here (for example Matrixyl, Argireline, Syn-Ake) are the property of their respective owners and are used only to identify the ingredient under discussion. Their appearance implies no affiliation with, or endorsement by, the proprietor.
Evidence changes
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Identity
the only human cathelicidin — a 37-amino-acid, cationic, amphipathic α-helical peptide that is a core effector of innate immunity. It's produced as an inactive precursor (hCAP18) by keratinocytes, neutrophils and other cells, then cleaved by proteases (kallikreins KLK5/KLK7) into the active LL-37. Its production is induced by vitamin D (UV light → vitamin D → cathelicidin — one reason facial skin is a hotspot) and by an alternative ER-stress pathway. It sits in the skin's chemical barrier — the first line of defense against microbes.
Mechanism (as proposed)
LL-37 is cationic and amphipathic, so it's drawn to negatively-charged microbial membranes, which it inserts into and disrupts, killing bacteria rapidly and broadly (its antimicrobial face). But the same peptide is a host immunomodulator/"alarmin": it chemoattracts immune cells, promotes angiogenesis and wound repair, and — critically — binds host nucleic acids (self-DNA/RNA) and ferries them into immune cells, where they activate Toll-like receptors (notably TLR9). In healthy skin this is controlled; when cathelicidin is over-expressed (psoriasis) or mis-processed into inflammatory fragments (rosacea) or released in NETs (lupus), it breaks immune tolerance and ignites chronic inflammation/autoimmunity. So LL-37's healing and harming functions are two faces of one molecule — which is exactly why exogenous use is not a simple "healing peptide" proposition.
Chemical identifiers
Cross-reference identifiers for the authoritative external databases — not a recipe, and nothing about how to use it.
InChIKeyPOIUWJQBRNEFGX-XAMSXPGMSA-N
SMILESCC[C@H](C)[C@@H](C(=O)NCC(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](CC1=CC=CC=C1)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CCCNC(=N)N)C(=O)N[C@@H]([C@@H](C)CC)C(=O)N[C@@H](C(C)C)C(=O)N[C@@H](CCC(=O)N)C(=O)N[C@@H](CCCNC(=N)N)C(=O)N[C@@H]([C@@H](C)CC)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CC(=O)O)C(=O)N[C@@H](CC2=CC=CC=C2)C(=O)N[C@@H](CC(C)C)C(=O)N[C@@H](CCCNC(=N)N)C(=O)N[C@@H](CC(=O)N)C(=O)N[C@@H](CC(C)C)C(=O)N[C@@H](C(C)C)C(=O)N3CCC[C@H]3C(=O)N[C@@H](CCCNC(=N)N)C(=O)N[C@@H]([C@@H](C)O)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](CO)C(=O)O)NC(=O)[C@H](CCCCN)NC(=O)[C@H](CCC(=O)O)NC(=O)[C@H](CCCCN)NC(=O)[C@H](CO)NC(=O)[C@H](CCCCN)NC(=O)[C@H](CCCNC(=N)N)NC(=O)[C@H](CC4=CC=CC=C4)NC(=O)[C@H](CC5=CC=CC=C5)NC(=O)[C@H](CC(=O)O)NC(=O)CNC(=O)[C@H](CC(C)C)NC(=O)[C@H](CC(C)C)N
via PubChem exact-name match (LL-37) · high confidence
Sources — 4 cited
01Reinholz M, Ruzicka T, Schauber J. Cathelicidin LL-37: an antimicrobial peptide with a role in inflammatory skin disease. Ann Dermatol. 2012 (dual role; rosacea/psoriasis/AD; vitamin D & ER-stress induction).
02Lande R, et al. Cationic antimicrobial peptides in psoriatic skin cooperate to break innate tolerance to self-DNA. (LL-37 + self-DNA → TLR9/pDC); LL-37 as psoriasis T-cell autoantigen.
03Yamasaki K, Di Nardo A, Gallo RL, et al. — cathelicidin processing (KLK5/KLK7) and pro-inflammatory fragments in rosacea.
04Reviews: innate immunity & cathelicidin in inflammatory skin disease (PMC3904447); LL-37 as a "double-edged sword" (host defense vs disease). (Exogenous therapeutic use preclinical; no human approvals as of 2026.)
Updated 2026-07-13 (watch: engineered LL-37 analogs/fragments that dissociate antimicrobial from pro-inflammatory activity — the field's key therapeutic goal)
Grades reflect the published evidence, not our interest. No dosing, reconstitution, or administration is published for research compounds — that restraint is deliberate.
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Region — International
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