LL-37 is the only cathelicidin made by humans, a 37-amino-acid peptide that forms part of the body’s first line of defense against infection.[1] It kills microbes, signals immune cells and helps wounds close. It has been tested as a topical wound treatment with mixed results,[3][4] and it has also been linked to rosacea, psoriasis and cancer.[6][8][11] No LL-37 product is approved, and FDA has listed safety concerns about compounded versions.[14]
What is LL-37?
LL-37 is cut from a larger protein called hCAP18. Its name comes from its first two amino acids (two leucines, “LL”) and its length of 37 amino acids.[12] It is made in the skin, gut, airways and testes, and by white blood cells including neutrophils, monocytes, T cells and B cells.[1]
Its known roles include:[1]
- Killing a broad range of bacteria and other microbes
- Binding and neutralizing bacterial toxins (LPS)
- Calling immune cells to wounds and infection sites
- Helping skin grow back over wounds
For other peptides studied for immune effects, see our immune peptides page.
LL-37 and wound healing
In healthy skin, hCAP18/LL-37 levels rise sharply after wounding, peaking at about 48 hours. Swedish researchers found it was missing from the edge of chronic ulcers, and blocking LL-37 slowed skin regrowth in lab-grown human skin.[2] That led to clinical trials:
| Trial | People | Result |
|---|---|---|
| Sweden, 2014 (phase 1/2) | 34 with venous leg ulcers | At 0.5 mg/mL, healing rate about 6 times faster than placebo and ulcer area down 68%; 1.6 mg/mL cut area 50%; 3.2 mg/mL no better than placebo[3] |
| Poland and Sweden, 2021 (phase 2b) | 148 with venous leg ulcers | No significant overall benefit vs placebo; post hoc signal in ulcers of at least 10 cm²[4] |
| Indonesia, 2023 | People with mildly infected diabetic foot ulcers | More healing (granulation) tissue with LL-37 cream; no difference in inflammation markers or bacteria[5] |
The 2021 trial report is copyrighted by Promore Pharma, which was developing LL-37 as ropocamptide, and one author held shares in the company.[4]
Can LL-37 fight infections?
In lab studies LL-37 kills a broad range of microbes,[1] and immune cells use it to kill tuberculosis bacteria.[10] That has made it popular online as an “immune” peptide. However, we found no published human trial testing LL-37 as a treatment for infection. In the diabetic foot ulcer trial, LL-37 cream did not reduce bacterial counts more than placebo by the end of 4 weeks.[5]
LL-37 in rosacea and psoriasis
LL-37 is not always helpful. Too much, or the wrong form, may drive skin inflammation:
- Rosacea: people with rosacea have abnormally high cathelicidin levels in facial skin, processed into different fragments than in healthy skin. Injecting those fragments into mice caused skin inflammation.[6]
- Psoriasis: LL-37 binds the body’s own DNA and turns it into a strong trigger for interferon-producing immune cells.[7] About two-thirds of people with moderate-to-severe plaque psoriasis had T cells that target LL-37, and these were linked to disease activity.[8]
The vitamin D link
The gene for LL-37 has a vitamin D response element, and active vitamin D directly switches it on in skin cells, monocytes and neutrophils.[9] In human macrophages, immune sensing of bacteria raised vitamin D activation, which induced cathelicidin and helped kill tuberculosis bacteria. Blood with low vitamin D levels was less able to support this response.[10]
LL-37 and cancer: findings both ways
LL-37’s role in cancer depends on the tissue:[11]
- May promote: ovarian, lung and breast cancers. In mice, blocking LL-37 slowed the growth of ovarian tumor grafts by reducing the recruitment of supporting stromal cells.[12]
- May suppress: colon and gastric cancers. LL-37 triggered death of colon cancer cells, and mice lacking cathelicidin developed more chemically induced colon tumors.[13]
These are mostly lab and animal results. MD Anderson ran a small study injecting LL-37 into melanoma tumors; posted results cover only 3 people, so it says little about benefit.[17]
LL-37 dosage
There is no approved or established dose. Studies used:
| Setting | Amount |
|---|---|
| Venous leg ulcers | 0.5, 1.6 or 3.2 mg/mL on the wound twice weekly for 4 weeks[3] |
| Diabetic foot ulcers | Cream twice weekly for 4 weeks[5] |
| Melanoma | 250 to 500 micrograms injected into each tumor weekly, up to 8 weeks[17] |
In the leg ulcer trial, the highest dose worked no better than placebo.[3] Injections under the skin for general use have not been tested. Our peptide calculator can convert a vial’s milligrams into syringe units, but that does not make an untested dose safe.
LL-37 side effects and safety
- Topical trials: the wound trials reported no safety concerns, and LL-37 was well tolerated at both doses in the larger trial.[3][4]
- Injections: in the small melanoma study, no serious adverse events were recorded.[17]
- FDA’s concerns: compounded LL-37 may trigger immune reactions depending on the route, may have impurity problems, and FDA lacks enough safety data to know whether it would harm people. Nonclinical findings suggest harm to male reproduction and that LL-37 can promote tumors in some tissues.[14]
- Inflammation: because excess LL-37 is linked to rosacea and psoriasis, raising it is not automatically beneficial.[6][8]
LL-37 vs KPV
Both are immune-related peptides sold online. LL-37 is a natural antimicrobial peptide with small human wound trials,[3] while KPV is a much smaller, three-amino-acid peptide with a different and mostly preclinical evidence base. They are not interchangeable. For other immune peptides, see thymosin alpha-1; for wound-repair peptides, see BPC-157.
Is LL-37 legal or FDA approved?
- Not approved: LL-37 has reached only phase 2 wound trials, and no LL-37 drug has been approved.[4]
- Compounding: FDA’s safety-risk page lists cathelicidin LL-37 among substances previously in category 2 whose nominations were withdrawn, and still describes its safety concerns.[14] It does not appear on FDA’s May 2026 list of nominated substances.[15]
- Advisory committee: FDA says its Pharmacy Compounding Advisory Committee will discuss LL-37 for the 503A bulks list at a meeting before the end of February 2027.[16]
- Sport: LL-37 is not named on WADA’s 2026 Prohibited List. In our reading, as a substance without approval for human therapeutic use it would fall under the S0 category, which is banned at all times.[18]
This is general information, not legal advice.
