At a glance

What is LL-37?

LL-37 is the active 37-amino acid fragment of the only human cathelicidin, a natural host-defense (antimicrobial) peptide produced by immune and skin cells. It is a well-studied part of the body's innate immune system. It is sold through wellness and "research peptide" channels for antimicrobial and immune support, and it is not an approved medicine.

How does it work?

LL-37 has two broad actions. Its positively charged, membrane-active structure can directly disrupt the membranes of microbes, and it also modulates the immune system, influencing immune-cell recruitment, inflammation, and wound healing, and binding some microbial factors. These roles are documented in a large laboratory and animal literature. Importantly, its effects are context-dependent: it can be either pro- or anti-inflammatory and has been implicated in some inflammatory skin diseases. This describes its biology, separate from demonstrated benefit from giving it as a therapy.

Is it FDA-approved?

No. There is no FDA-approved exogenous LL-37 therapeutic, and gray-market versions are unapproved. It was not among the peptides reviewed favorably at the 2026 FDA compounding advisory meetings.

What does the research show?

The evidence is preclinical for any injected wellness use. LL-37's biology in innate immunity, wound healing, and skin disease is documented in humans and in extensive laboratory work, including studies of how it disrupts microbes and binds microbial factors (example¹).

However, there are no controlled human trials establishing efficacy or safety of self-administered LL-37 for antimicrobial, immune, or healing wellness uses, and its context-dependent, sometimes pro-inflammatory, behavior argues against simple benefit claims.

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