What is LL-37 used for?

LL-37 is researched for potential applications in treating infections, promoting wound healing, and modulating immune responses. It is not approved for therapeutic use.

Is LL-37 an antibiotic?

LL-37 is an antimicrobial peptide with activity against bacteria, but it's not a conventional antibiotic. It works by disrupting microbial membranes and has immunomodulatory effects beyond direct killing.

Can LL-37 be harmful?

While LL-37 has beneficial antimicrobial effects, it can also promote inflammation in certain contexts. Elevated LL-37 is implicated in conditions like psoriasis. Its effects are context-dependent.

Fact-checked by the Peptide Authority Editorial Board · Last reviewed: 1 February 2026

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Immune & Inflammatory•Updated 2026-02-01•5 min read

What Is LL-37? Benefits, Research & Safety

The only human cathelicidin antimicrobial peptide, with broad-spectrum antimicrobial activity and important immunomodulatory functions.

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Also known as:

Human Cathelicidin

CAP18

hCAP18

DAnimal/cell evidence onlyUK: Sold as 'research only' (UK)WADA: Sport status unclear

UK summary: Not a licensed UK medicine. Endogenous antimicrobial peptide investigated for chronic infections, wound healing, and inflammation. Substantial preclinical literature; human therapeutic use is essentially absent.

Quick Facts

Overview

LL-37 is the only cathelicidin antimicrobial peptide (CAMP) found in humans. It is a 37-amino acid peptide derived from the C-terminal portion of the 18 kDa human cathelicidin protein (hCAP18). The name "LL-37" refers to its 37 amino acids and the two leucine residues at its N-terminus. LL-37 is produced by various immune cells (neutrophils, macrophages, epithelial cells) and plays crucial roles in innate immunity. It has direct antimicrobial activity against a broad spectrum of pathogens including bacteria, viruses, and fungi. Beyond direct killing, LL-37 also modulates immune responses, influences wound healing, and affects angiogenesis. The peptide has attracted research interest for its potential therapeutic applications in infectious diseases, wound healing, and inflammatory conditions. However, LL-37 is a complex molecule with multiple activities, and its effects can vary depending on concentration, tissue environment, and disease context. LL-37 is not approved for therapeutic use and remains primarily a research compound. Deficiencies or dysregulation of LL-37 have been implicated in various diseases, highlighting its importance in health and disease.

Evidence standards summary

LL-37 — evidence and risk at a glance

Twenty standard modules scored against the Peptide Authority evidence grading methodology. Missing modules indicate the field has not yet been characterised editorially — treat absences as uncertainty rather than reassurance.

01Evidence snapshot

DAnimal/cell evidence onlyOverall grade against our evidence grading methodology.

Not a licensed UK medicine. Endogenous antimicrobial peptide investigated for chronic infections, wound healing, and inflammation. Substantial preclinical literature; human therapeutic use is essentially absent.

02Human evidence grade

ETheoretical / insufficientStrength of evidence from published human trials.

03Preclinical evidence grade

BModerate human evidenceAnimal-model and in-vitro evidence quality.

04Regulatory status

UK: Not licensed for human use. Research compound only.
EU: Not approved for therapeutic use.
Notes: LL-37 is a research compound with no regulatory approvals. Therapeutic development continues but the peptide's complexity presents challenges.

05Approved medical uses

None in the UK or EU as a finished medicine. (Or: not yet documented; treat as absence rather than approval.)

06Unapproved / promotional claims

Treats antibiotic-resistant infections.
Cures chronic Lyme or biofilm-based infections.
Heals wounds faster than standard NHS care.
Safe and effective long-term antimicrobial therapy.

07Common internet claims

Marketed by 'functional medicine' clinics for chronic Lyme / biofilm infections.
Sold by online retailers as a research-only antimicrobial peptide.
Promoted as the natural answer to antibiotic resistance.

08Claim vs evidence

Claim	Evidence	Human evidence?	Regulatory concern	Safer wording
“Treats chronic infections antibiotics can't”	D	No	High	Mechanistic and animal-model evidence; no human RCT support for antibiotic-resistant infection treatment.
“Heals wounds faster than standard care”	D	No	High	Animal wound-healing data exist; no human RCT vs standard care.

09Safety uncertainty score

High

Limited human safety data; meaningful uncertainty about rare or long-term effects.

10Known adverse signals

Pro-inflammatory and immunomodulatory effects — can amplify inflammation.
Theoretical risk in autoimmune disease.
Injection-site reactions.
Unknown effects of sustained exogenous cathelicidin exposure.

11Drug-interaction uncertainty

High

Interaction picture sparse; meaningful uncertainty when combined with other medicines.

12Anti-doping status

WADA: Sport status unclearWADA strict-liability framing applies.

13UK legal position

UK: Sold as 'research only' (UK)

Not licensed for human use. Research compound only.

Read the full UK legal guide → Research peptides and UK law

14EU legal position

Not approved for therapeutic use.

15What this page cannot tell you

Whether a UK-purchased vial contains LL-37 at the labelled concentration.
Whether the antimicrobial mechanism translates from petri dish to human infection.
Long-term effects of sustained antimicrobial peptide elevation.
Whether it interacts with prescribed antibiotics or immunosuppressants.

16Last reviewed

Last reviewed: 1 February 2026

Next review due: 1 February 2027

Spotted an error or something out of date? Send a correction.

17Citation quality score

CLimited human evidenceQuality of the sources we cite, graded against the evidence grading methodology.

18Research gaps

No registered Phase 2 or 3 trials in humans for any indication.
Antimicrobial in vitro activity does not equal clinical effectiveness.
Long-term safety entirely unstudied.
Combination with conventional antibiotics uncharacterised.

19Safer alternatives / established care pathways

GP and infectious-diseases referral for suspected chronic infection.
NHS antimicrobial-stewardship pathway for resistant infections.
NHS wound clinic for non-healing wounds — substantial evidence-based options exist.

20Doctor discussion prompts

Questions to ask a qualified clinician

These are starter questions you can adapt for a GP, specialist, pharmacist, or anti-doping advisor. The aim is to help you have a better-informed conversation — not to replace one.

Is LL-37 a licensed UK medicine?
What licensed treatments exist for the infection or wound concern I have?
Why is mechanistic plausibility not the same as proven benefit here?

Discovery & History

Cathelicidins were first discovered in the early 1990s as a family of antimicrobial peptides found in various mammalian species. In 1995, human cathelicidin (hCAP18) was identified in neutrophils. Researchers discovered that hCAP18 requires proteolytic processing to release the active antimicrobial peptide. The active portion, LL-37, was characterised and found to have broad-spectrum antimicrobial activity. Subsequent research revealed that LL-37's functions extended beyond direct antimicrobial killing. Studies demonstrated immunomodulatory effects, influence on wound healing, and roles in inflammatory responses. This multifunctionality has made LL-37 an intensively studied peptide. Research has also identified associations between LL-37 levels and various diseases. Deficiency is associated with increased susceptibility to infections, while overexpression or dysregulation may contribute to autoimmune conditions like psoriasis. The peptide's complexity—beneficial antimicrobial effects but potential for inflammatory damage in some contexts—has made therapeutic development challenging but continues to be an active area of research.

Mechanism of Action

LL-37 exerts its effects through multiple mechanisms: **Direct Antimicrobial Activity** LL-37 is cationic and amphipathic, allowing it to interact with and disrupt negatively charged bacterial membranes. It can kill bacteria, enveloped viruses, and fungi through membrane permeabilisation and other mechanisms. **Lipopolysaccharide (LPS) Neutralisation** The peptide can bind to and neutralise bacterial LPS (endotoxin), potentially reducing inflammation triggered by Gram-negative bacterial infections. **Immunomodulation** LL-37 affects immune cell function in multiple ways: - Chemoattraction of immune cells - Modulation of cytokine production - Influence on dendritic cell maturation - Effects on T cell responses **Wound Healing Promotion** LL-37 promotes wound healing through effects on epithelial cell migration, proliferation, and angiogenesis. It can stimulate re-epithelialisation of wounds. **Angiogenesis** The peptide can promote new blood vessel formation, which is relevant to wound healing but also potentially to tumour biology. **Biofilm Disruption** LL-37 can disrupt bacterial biofilms, potentially enhancing the effectiveness of antibiotics against biofilm-associated infections.

Researched Benefits

Based on preclinical and clinical research findings:

1
Broad-spectrum antimicrobial activity against bacteria, viruses, and fungi
2
LPS neutralisation reducing sepsis-related inflammation
3
Wound healing promotion
4
Biofilm disruption
5
Immunomodulatory effects
6
Potential applications in infection control

Claim vs Evidence

How popular claims about LL-37 stack up against the current research, graded using our public evidence grading methodology.

Claim	Evidence	Human evidence?	Regulatory concern	Safer wording
“Treats chronic infections antibiotics can't”	D	No	High	Mechanistic and animal-model evidence; no human RCT support for antibiotic-resistant infection treatment.
“Heals wounds faster than standard care”	D	No	High	Animal wound-healing data exist; no human RCT vs standard care.

Theoretical Dosing & Protocols

⚠️ Educational Only: The following information is derived from research literature and is not a prescription or recommendation. No standardised human dosing exists. Always consult a qualified healthcare professional.

Theoretical Dosage	Not established; highly variable in research
Frequency	Variable depending on application
Duration	Variable
Notes	LL-37 is not approved for therapeutic use. Research applications vary widely depending on the condition being studied. The peptide's complex biology makes dosing and application challenging.

Administration Routes

Routes studied in research settings (educational only):

Topical (wound healing research)
Injection (various research applications)
Inhaled (respiratory research)

Half-Life	Stability
Short; subject to proteolytic degradation in vivo	Requires careful handling; susceptible to degradation

Safety Profile & Known Risks

Commonly Reported Side Effects

Limited human safety data
Potential for local irritation at high concentrations

Rare Risks & Concerns

Pro-inflammatory effects in certain contexts
Potential to exacerbate autoimmune inflammation
Unknown long-term effects

Contraindications

Psoriasis (LL-37 implicated in pathogenesis)
Certain autoimmune conditions
Pregnancy (no safety data)
Active malignancy (angiogenic effects)

UK & EU Regulatory Context

🇬🇧 United Kingdom

Not licensed for human use. Research compound only.

🇪🇺 European Union

Not approved for therapeutic use.

LL-37 is a research compound with no regulatory approvals. Therapeutic development continues but the peptide's complexity presents challenges.

Clinical Studies Summary

Cationic antimicrobial peptides and periodontal physiopathology: A systematic review.

Data remain inconsistent between the studies for hBDs mainly due to heterogeneity of the results, periodontal disease diagnostic criteria and assaying technique employed. Given their role in innate immunity and their antimicrobial functions, LL-37 and α-defensins may be eligible as periodontal clinical biomarkers and could be an interesting way for therapeutic development.

J Periodontal Res. 2019View on PubMed

Acute salivary antimicrobial peptide secretion response to different exercise intensities and durations.

Levels of four salivary antimicrobial peptides increased after exercise dependently or independently of exercise intensity and duration, whereas some salivary antimicrobial peptides did not change after exercise. These findings suggest that the secretory responses to acute exercise with different intensities and durations differ among salivary antimicrobial peptides.

Am J Physiol Regul Integr Comp Physiol. 2024View on PubMed

The therapeutic efficacy of Bifidobacterium animalis subsp. lactis BB-12(®) in infant colic: A randomised, double blind, placebo-controlled trial.

Supplementation with BB-12 is effective in managing infant colic. The effect could derive from immune and non-immune mechanisms associated with a modulation of gut microbiota structure and function.

Aliment Pharmacol Ther. 2020View on PubMed

Antimicrobials from human skin commensal bacteria protect against Staphylococcus aureus and are deficient in atopic dermatitis.

Strikingly, reintroduction of antimicrobial CoNS strains to human subjects with AD decreased colonization by S. aureus These findings show how commensal skin bacteria protect against pathogens and demonstrate how dysbiosis of the skin microbiome can lead to disease.

Sci Transl Med. 2017View on PubMed

LL-37: Biological Mechanisms and Emerging Therapeutic Applications in Intestinal Disease.

We have further explored new strategies to overcome these challenges in the near future, including peptide engineering, nanocarrier delivery systems, and combined therapy. These findings together position LL-37 at the intersection of intestinal immunity and microbial ecology, providing a theoretical basis for its therapeutic application in IBD, CRC and infectious colitis.

Immun Inflamm Dis. 2026View on PubMed

β-Amyloid (Aβ) and Human Cathelicidin LL-37: Two Sides of the Same Coin?

Similarly to Aβ, LL-37 can induce neuroinflammation by stimulating human microglia to release inflammatory cytokines, such as TNF-α and IL-6. Neuroinflammation is essential for protecting the brain from pathogens-when prolonged, it drives pathological processes underlying AD, Parkinson's disease (PD), and other neurodegenerative disorders.

Int J Mol Sci. 2026View on PubMed

Registered Trials & Regulatory Status

Registered trials

Currently recruiting

Furthest phase

Phase 2

Approved product

7 of 9 completed trials have never posted results. Unreported trials are not neutral: results that go unpublished are more often negative ones.

Evaluation of 25(OH)D3 and LL-37 Levels in Periimplant Sulcus Fluid

N/A

Status: Not Yet Recruiting · 72 participants · Recep Tayyip Erdogan University

Conditions: Peri Implantitis, Peri Implant Mucositis

No results postedNCT07280754

Cathelicidin LL-37 Relation to Potentially Malignant Lesions

N/A

Status: Completed · 45 participants · Fayoum University

Conditions: Oral Potentially Malignant Lesions

No results postedNCT06219330

Chlorhexidine and Essential Oil Mouthwashes on Human Beta-Defensin 2 (hbD2) and Kathelicidin (LL-37) Saliva Levels

N/A

Status: Unknown · 120 participants · Istanbul Medeniyet University

Conditions: Mouth and Tooth Diseases, Periodontal Diseases, Gingivitis

No results postedNCT04946617

The Role of Anti-inflammatory Cytokines and Antimicrobial Peptide LL-37 Biomarkers in the Treatment of Periodontal Disease.

N/A

Status: Completed · 60 participants · Universidad Rey Juan Carlos

Conditions: Periodontal Diseases, Periodontitis

No results postedNCT04404335

Peri-implant Vitamin D and Cathelicidin (LL-37) Levels

N/A

Status: Completed · 33 participants · Altinbas University

Conditions: Peri-Implantitis and Peri-implant Mucositis

No results postedNCT06867250

Cathelicidin LL-37 Levels in the GCF and the Saliva of Smokers and Non-smokers With Stage III,IV Periodontitis

N/A

Status: Completed · 60 participants · Cairo University

Conditions: Smoking Reduction

No results postedNCT04861493

Efficacy of LL-37 Cream on Bacteria Colonization, Inflammation Response and Healing Rate of Diabetic Foot Ulcers

PHASE2

Status: Unknown · 40 participants · Fakultas Kedokteran Universitas Indonesia

Conditions: Diabetic Foot Ulcer

No results postedNCT04098562

Salivary TAS, TOS, LL-37 and Dental Status in Passive Smoking Children

N/A

Status: Completed · 180 participants · Merve Erkmen Almaz

Conditions: Passive Smoking, Oxidative Stress, Dental Caries

No results postedNCT04292548

Passive Smoking and LL-37 in Children

N/A

Status: Completed · 180 participants · Kırıkkale University

Conditions: Innate Immunity, Periodontal Health

No results postedNCT03639376

Intratumoral Injections of LL37 for Melanoma

PHASE1/PHASE2

Status: Completed · 4 participants · M.D. Anderson Cancer Center

Conditions: Melanoma

Results postedNCT02225366

Effects of Smoking and Vitamin D3 on the Levels of Human Cathelicidin Peptide LL-37

N/A

Status: Completed · 60 participants · Gazi University

Conditions: Periodontitis

No results postedNCT03923218

Effects of Vitamin D and Omega-3 Fatty Acids on Infectious Diseases and hCAP18 (VITAL Infection)

Status: Active Not Recruiting · 25,874 participants · Brigham and Women's Hospital

Conditions: Infections, Human Cathelicidin Antimicrobial Peptide (hCAP-18)

No results postedNCT01758081

Adverse event reports (FDA FAERS)

Not applicable: no licensed product contains this peptide, so it is not reported through FAERS. This is an absence of surveillance, not evidence of safety.

Source: ClinicalTrials.gov and openFDA. Updated automatically.

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Frequently Asked Questions

Questions to ask a qualified clinician about LL-37