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LL-37 (Cathelicidin): What the Evidence Actually Shows

Grade CNo approval

The short version

  • The only cathelicidin found in humans, part of innate immune defence.
  • Directly antimicrobial and also an immune signalling molecule.
  • Its effects are genuinely double-edged. Elevated LL-37 is implicated in rosacea and psoriasis.
  • Vitamin D regulates its expression, which is a large part of the vitamin D and immunity story.
  • No approval. Sold for biofilm and chronic infection protocols.

What it is

LL-37 is produced by neutrophils and epithelial cells as part of first-line immune defence. It disrupts bacterial membranes directly, and separately acts as a signalling molecule recruiting immune cells. Its expression is upregulated by vitamin D, which is one of the more concrete mechanisms behind vitamin D's association with immune function.

The part that gets left out

LL-37 is not straightforwardly beneficial. Elevated LL-37 is implicated in the pathology of rosacea, where it drives inflammation, and it has a recognised role in psoriasis, where it can form complexes with self-DNA and trigger autoimmune activation. It has also been studied in the context of certain cancers with mixed directionality.

A compound with a documented role in driving inflammatory skin disease is not one to administer casually, and anyone with rosacea, psoriasis or an autoimmune condition should treat it as contraindicated pending advice from a specialist.

What this will not do

Related

Full library · Safety and sourcing · Reconstitution calculator · The 2026 regulatory picture

Regulatory status current as of the page date. This area is changing quickly and this page is reviewed monthly.