Research
What Is LL-37? The Body’s Own Antimicrobial Peptide
LL-37 is part of your body’s built-in defense against bacteria, viruses and fungi. It is the only member of the cathelicidin family of antimicrobial peptides found in humans. Researchers are interested in it for hard-to-treat infections and slow-healing wounds, but it also plays a role in inflammatory skin diseases. This guide explains what LL-37 is, what the research shows, and the risks that come with it.
Reviewed for accuracy · Last reviewed October 19, 2026
What Is LL-37?
LL-37 is a 37-amino-acid peptide that begins with two leucines, which is where its name comes from. It is cut from a larger protein called hCAP18 and is produced by white blood cells, skin cells and the cells lining the gut, lungs and urinary tract.
It belongs to a class called host defense peptides, which are part of the innate immune system, the fast, non-specific first line of defense against infection.
How Does LL-37 Work?
- Punches holes in microbes: LL-37 is positively charged and is attracted to the negatively charged membranes of bacteria, which it disrupts.
- Fights biofilms: in lab studies, it helps break up biofilms, the protective slime layers that make some infections resistant to antibiotics.
- Signals the immune system: it attracts immune cells to infection sites and adjusts inflammatory signals.
- Supports healing: it promotes the growth of new blood vessels and the movement of skin cells into wounds.
Vitamin D connection. The gene for LL-37 is switched on by vitamin D. This is one reason researchers have linked low vitamin D levels to higher infection risk.
What Does the Research Show?
Infections. In lab and animal studies, LL-37 kills a broad range of bacteria, including some antibiotic-resistant strains, and disrupts biofilms. Turning it into a drug has been difficult because it breaks down quickly and can damage human cells at high concentrations.
Leg ulcers. A small randomized phase 1/2 trial (Grönberg et al., 2014) applied LL-37 to hard-to-heal venous leg ulcers. Ulcers in the LL-37 groups shrank faster than with placebo, and the treatment was well tolerated. Larger confirmatory trials have not changed its status.
A double-edged role. LL-37 is not purely protective. In psoriasis and rosacea, excess LL-37 helps drive skin inflammation, and in some autoimmune conditions it can help trigger the immune system against the body’s own DNA. In cancer research, it appears to promote some tumor types and suppress others.
| Area | What studies show | Evidence type |
|---|---|---|
| Bacteria and biofilms | Broad antimicrobial and antibiofilm activity | Lab and animal |
| Venous leg ulcers | Faster healing vs placebo | Small human RCT |
| Psoriasis and rosacea | Contributes to inflammation | Human tissue studies |
| Cancer | Promotes some tumors, suppresses others | Lab and animal |
LL-37 Safety and Side Effects
Because LL-37 can both fight infection and drive inflammation, its effects depend heavily on context. Potential concerns raised in research include worsening of inflammatory skin conditions, effects on autoimmune disease, and possible effects on certain cancers. The leg ulcer trial reported good tolerability for topical use, but there is no good safety data for injected research-grade LL-37.
Is LL-37 FDA-Approved?
No. LL-37 is not approved by the FDA for any use, and it is not on the 503A Bulks List.
In April 2026, the FDA moved this substance out of its “Category 2” table of compounding ingredients that may present significant safety risks and into a separate table of substances whose nominations were withdrawn by the nominators. That move is not a finding that the substance is safe or effective, and it does not place it on the 503A Bulks List.
LL-37 vs Other Immune and Repair Peptides
| Compound | Main role | Human evidence |
|---|---|---|
| LL-37 | Antimicrobial, antibiofilm, wound repair | Small leg-ulcer trial |
| Thymosin alpha-1 | T-cell immune modulation | Several RCTs; approved abroad |
| KPV | Anti-inflammatory (α-MSH fragment) | Lab and animal |
| BPC-157 | Tissue repair | Mostly animal |
| GHK-Cu | Skin remodeling, wound repair | Cosmetic and lab studies |
LL-37 vs antibiotics. Bacteria rarely develop resistance to antimicrobial peptides as quickly as they do to many antibiotics, which is why LL-37 and its synthetic relatives are being studied as templates for new anti-infective drugs.
LL-37 vs KPV. Both are discussed for gut and skin health, but they work in opposite directions in some settings: KPV is purely anti-inflammatory, while LL-37 can increase inflammation in conditions like psoriasis.
Buying Research-Grade LL-37: What to Check
Products sold as LL-37 by research suppliers are laboratory chemicals, not medicines. They are not made under drug manufacturing rules, so quality varies a lot between vendors. If you are evaluating an LL-37 supplier for lab research, these are the checks that matter:
- Batch-specific COA: the certificate should match the lot number on your vial, not a generic sample.
- Independent lab: testing should come from a named third-party lab, ideally with a way to verify the report online.
- Identity, not just purity: HPLC purity alone does not confirm the right molecule; look for mass spectrometry (MS) identity confirmation.
- Endotoxin and sterility results: these matter for any injectable research material.
- Correct fill amount: the measured content should be close to the labeled milligrams.
Our Trusted Sources page lists vendors we track, with current community codes. Our guide to reading a certificate of analysis explains each line of a COA.
Key Takeaways
- LL-37 is the only human cathelicidin, a natural antimicrobial peptide.
- It kills bacteria, disrupts biofilms and supports wound healing in lab studies.
- A small trial found faster healing of venous leg ulcers.
- It also drives inflammation in psoriasis and rosacea and has mixed effects in cancer.
- It is not FDA-approved.
Frequently Asked Questions
What is LL-37?
LL-37 is a 37-amino-acid antimicrobial peptide made by the human body. It is the only human member of the cathelicidin family.
What does LL-37 do?
It kills bacteria and other microbes, disrupts biofilms, attracts immune cells and supports wound healing.
Is LL-37 linked to vitamin D?
Yes. Vitamin D switches on the gene that produces LL-37.
Can LL-37 cause inflammation?
Yes. Excess LL-37 contributes to inflammation in psoriasis and rosacea and may play a role in some autoimmune conditions.
Is LL-37 FDA-approved?
No. It is not approved for any use and is not on the 503A Bulks List.
Sources
- Grönberg et al. (2014), Wound Repair and Regeneration – Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers
- Vandamme et al. (2012) – A comprehensive summary of LL-37, the factotum human cathelicidin peptide
- Lande et al. (2007), Nature – Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide (LL-37)
- FDA – Certain bulk drug substances for use in compounding that may present significant safety risks (updated April 22, 2026)
MLCR SCTY provides educational information, not medical or legal advice. Research-use-only products are not intended for human consumption.