What it is
LL-37 is the only human member of the cathelicidin family of antimicrobial peptides. The body makes it in skin, the gut, the lungs and white blood cells.
It can damage bacteria directly and also helps signal the immune system. Too much of it has been linked to inflammatory skin conditions such as rosacea and psoriasis.
US regulatory status
Not FDA-approved. The FDA removed it from its Category 2 compounding list in April 2026, with an advisory committee review planned by early 2027; it is not currently an accepted bulk substance for compounding.
What the research shows
Most research is in cells and animals. A small clinical trial tested LL-37 applied to hard-to-heal leg ulcers with some promising signals, but there are no large trials and no good human data for injected use.
How it is given
Subcutaneous injection or topical (unapproved)
Commonly reported side effects
- Injection site redness or irritation
- Possible skin inflammation
- Limited human safety data
- Risk of contaminated or mislabeled products
Questions to ask your provider
- What does the research really show about LL-37 in humans?
- Are there FDA-approved treatments for my goal that have stronger evidence?
- What are the risks of products labeled "research use only," and how would I know what is really in them?