What does LL-37 peptide do?
LL-37 is the only human cathelicidin — kills bacteria, breaks down biofilms, and promotes wound healing. A meaningful cancer caution applies.
Updated May 11, 2026 · 4 min read
LL-37 is the only cathelicidin antimicrobial peptide expressed in humans — a 37-amino-acid fragment of the precursor protein hCAP18 that your immune system deploys at sites of infection and injury. It kills bacteria by disrupting their membranes, breaks down the protective biofilms that shelter bacteria from antibiotics, recruits immune cells to wound sites, and promotes the regrowth of skin and blood vessels. In the research peptide community it's used primarily for wound healing and skin applications, but it carries meaningful cautions — particularly around cancer — that set it apart from most other peptides in this space.
What LL-37 actually is
Your neutrophils, epithelial cells, and macrophages produce hCAP18, which gets cleaved at injury and infection sites to release the active fragment: LL-37. The name comes from its structure — it starts with two leucines (LL) and is 37 amino acids long.
This is one of the few peptides on this site with a clear natural human precedent. You're not adding a foreign signal; you're supplementing a molecule your body already uses. That said, your body tightly regulates how much LL-37 is produced and where — exogenous administration bypasses that regulation entirely.
The main things LL-37 does
Direct antimicrobial activity LL-37 disrupts the lipid membranes of bacteria (gram-positive and gram-negative), fungi, and some enveloped viruses. It's active against organisms that have developed resistance to conventional antibiotics — the mechanism (physical membrane disruption) isn't something bacteria can easily evolve resistance to.
Biofilm disruption Many chronic infections hide inside biofilms — structured communities of bacteria encased in a protective matrix that antibiotics can't penetrate well. LL-37 breaks down these biofilms and makes the bacteria inside more vulnerable. This is part of why research interest in LL-37 for chronic wound infections, sinusitis, and recurrent UTIs has grown.
Wound healing At injury sites, LL-37:
- Promotes re-epithelialization (regrowth of surface tissue)
- Stimulates angiogenesis (new blood vessel formation)
- Recruits keratinocytes, fibroblasts, and neutrophils to the repair zone
- Modulates the inflammatory cascade
For context, impaired LL-37 expression is associated with chronic non-healing wounds, particularly in diabetic foot ulcers — which is part of why topical LL-37 has been studied as a therapeutic.
Immune modulation LL-37 is both pro-inflammatory (at injury sites, it escalates the immune response) and anti-inflammatory (it helps resolve inflammation once infection is cleared). The context matters, which is why dosing matters — too much LL-37 in the wrong context causes an inflammatory flare.
The cancer caution — read this carefully
LL-37 has a documented pro-tumorigenic role in several cancer types. Research has found that LL-37 promotes tumor growth and metastasis in:
- Ovarian cancer
- Lung cancer
- Breast cancer (some subtypes)
In other cancers (colorectal, notably), LL-37 appears to have anti-tumor effects.
The mechanism is the same wound-healing biology: LL-37 promotes angiogenesis and cell migration — useful in healing, dangerous if tumor cells exploit those signals. This is not a theoretical concern based on one paper; it's a replicated finding across multiple research groups. Anyone with a current or recent cancer diagnosis, or significant family history of the relevant cancers, should not use LL-37 without specialist guidance.
How the research peptide community uses it
Because of the cancer caution and the inflammatory risk at higher doses, experienced users tend toward conservative dosing:
| Route | Typical dose | Notes |
|---|---|---|
| SubQ injection | 100–200 mcg, 3–5x/week | Most common; used for systemic or musculoskeletal wound support |
| Topical (compounded) | Concentration varies | Applied directly to wound or skin lesion |
| Intranasal | 100 mcg per nostril | Used for chronic sinusitis; less common |
Start low. LL-37 is a membrane-disrupting peptide — too much causes local tissue irritation and potentially a significant inflammatory reaction. Unlike BPC-157 or TB-500, there's less forgiveness in the dosing window.
Who is and isn't a candidate
Potentially appropriate (research context, not medical advice):
- Chronic wounds or skin ulcers that aren't responding to conventional care
- Recurrent sinus or skin infections with suspected biofilm component
- Athletes exploring antimicrobial peptide approaches to skin repair
Should avoid:
- Active cancer or remission from cancer types where LL-37 has pro-tumorigenic data
- Anyone immunocompromised (the immune-modulating effects are less predictable)
- People who've had significant allergic or inflammatory reactions to peptide injections
Verify peptide identity with a COA before using. See how to spot fake peptides.