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What it is
LL-37 is a 37-amino-acid peptide released from the human precursor protein hCAP18. Skin cells and several immune cells produce it as part of innate defense, especially around epithelial barriers, inflammation, and wounds.
Its name is easy to confuse with IL-37, an unrelated cytokine. Synthetic LL-37 has been studied as a topical wound treatment and in laboratory infection models. It is not an FDA-approved antibiotic, immune treatment, or injectable drug.
What people research it for
Early topical wound signal
Early human dataA 34-person randomized first-in-human trial found faster healing measures with two lower topical concentrations, while the highest concentration performed no better than placebo.
Larger trial was negative overall
Early human dataA 148-person phase 2b trial found no significant healing improvement in the full study population. A benefit appeared only in a post hoc subgroup with larger ulcers.
Broad laboratory antimicrobial activity
Preclinical / theorizedCell and microbiology studies report activity against multiple bacteria and biofilms, but physiological salt, proteases, toxicity, and bacterial adaptation limit direct translation.
Participates in normal wound biology
Animal studiesEndogenous LL-37 is present in acute wound defense and can affect keratinocyte migration, angiogenesis, and inflammatory signaling. That does not establish injected synthetic LL-37 as a healing treatment.
How it works
LL-37 carries a positive charge and can bind negatively charged microbial membranes. In laboratory systems it can disrupt membranes, affect biofilms, neutralize some microbial products, and interact with immune signaling pathways.
The same broad activity creates tradeoffs. Salt, proteins, and enzymes in living tissue can reduce antimicrobial activity, while higher exposure can injure human cells or amplify inflammation. LL-37 can also influence cell migration, blood-vessel growth, and wound repair, so its effects depend on tissue and concentration.
What the research actually shows
The first randomized human wound trial enrolled 34 people with hard-to-heal venous leg ulcers. After a placebo run-in, participants received topical LL-37 or placebo twice weekly for four weeks. Healing-rate estimates were about sixfold and threefold higher at the two lower concentrations, but the higher concentration showed no advantage over placebo.
A larger phase 2b trial randomized 148 people with difficult venous leg ulcers to two topical LL-37 concentrations or placebo alongside compression therapy for 13 weeks. The primary analysis found no significant healing improvement in the full population. A post hoc subgroup with wounds of at least 10 square centimeters showed signals that require a prospectively powered trial.
Both wound trials studied a controlled topical formulation applied to ulcers, not injection or general immune enhancement. The larger study described LL-37 as well tolerated at the tested topical concentrations, but that narrow result cannot establish systemic safety.
Laboratory reviews describe antibacterial and anti-biofilm activity against several organisms. They also identify major translation problems: reduced activity in physiological environments, rapid proteolysis, toxicity to human cells, manufacturing cost, and the ability of bacteria to develop adaptive resistance under repeated sub-inhibitory exposure.
LL-37 is also an immune signal rather than a simple antibiotic. Reviews link dysregulated endogenous LL-37 to inflammatory and autoimmune conditions, including psoriasis and lupus-related pathways. Depending on context it can recruit immune cells, bind nucleic acids, or amplify inflammation.
No controlled human evidence supports retail injectable LL-37 for chronic infection, Lyme disease, gut problems, immune boosting, or general recovery. A research vial is not equivalent to the sterile topical drug product tested in wound trials.
Handling & storage
Storage at a glance
Vendor consensus- Lyophilized
- -20°C or below
- Keep sealed and dry. ProSpec specifies below -18°C; AnaSpec specifies -20°C or lower.
- Reconstituted
- 4°C for 2 to 7 days, or aliquoted at -20°C or below for longer laboratory storage
- Manufacturer reagent guidance only. Avoid repeated freeze-thaw cycles.
- Light
- Keep sealed and protected from moisture and unnecessary light exposure.
- Room temperature
- ProSpec lists about 3 weeks for its sealed dry reagent, but this is not a universal shelf life.
- Reconstitution
- product-specified laboratory solvent
- AnaSpec lists water for its reagent. Other formulations may require different conditions.
Basis: Vendor consensus. Sources: ProSpec LL-37 technical page, AnaSpec LL-37 product data sheet
Two technical manufacturers agree that lyophilized LL-37 should be kept frozen near -20°C. AnaSpec also instructs laboratories to aliquot the prepared peptide and keep it at -20°C or lower, while ProSpec allows 4°C for only 2 to 7 days before longer frozen storage.
These are reagent instructions, not a clinical product label or a guarantee that a retail vial is sterile. Keep the material dry and protected from repeated freezing and thawing, and use the exact solvent and storage instructions supplied with the specific laboratory product.
Safety & cautions
LL-37 can damage mammalian cells at some concentrations and can promote or suppress inflammation depending on context. Potential systemic concerns include immune activation, tissue irritation, effects on blood vessels and cell growth, and unpredictable worsening of inflammatory or autoimmune disease. Human injection safety has not been established.
The wound trials used a purpose-built sterile topical formulation under medical supervision. Online lyophilized vials can differ in identity, purity, counter-ion, fill amount, sterility, and endotoxin burden. Antimicrobial activity in a dish does not make a product safe for treating an infection, and using it instead of proven antimicrobial care could delay effective treatment.
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Frequently asked questions
Is LL-37 an antibiotic?
It is a human host-defense peptide with antimicrobial activity in laboratory studies, but it is not an FDA-approved antibiotic.
Is LL-37 the same as IL-37?
No. LL-37 is a cathelicidin antimicrobial peptide. IL-37 is a different immune-signaling cytokine.
Has LL-37 been tested in people?
Yes, mainly as a controlled topical formulation for venous leg ulcers. The small trial was encouraging, but the larger phase 2b trial was negative in its full population.
Does LL-37 break down biofilms?
It has anti-biofilm activity in laboratory models. That does not prove that injected or topical retail LL-37 safely clears a human infection.
Is injectable LL-37 approved?
No. There is no FDA-approved injectable LL-37 product or established systemic treatment use.
Can LL-37 increase inflammation?
Yes. LL-37 can amplify or redirect immune signaling, and dysregulated endogenous LL-37 is linked to inflammatory and autoimmune pathways.
How should laboratory LL-37 be stored?
Checked technical suppliers specify frozen dry storage near -20°C. Prepared reagent should be kept only briefly at 4°C or divided into frozen aliquots according to the exact product instructions.
Sources
- First randomized LL-37 venous-ulcer trial
- Phase 2b LL-37 venous-ulcer trial
- Review of LL-37 antimicrobial and anti-biofilm research
- Review of LL-37 in inflammation and autoimmune disease
- ProSpec LL-37 technical page
- AnaSpec LL-37 product data sheet
Last reviewed September 17, 2026. This guide is educational and research-focused, not medical advice. LL-37 products referenced on PeptidePub are sold by third parties as materials for laboratory research use only, not for human or animal consumption.
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