What is LL-37?
LL-37 is the active C-terminal peptide generated from human cathelicidin hCAP18. It is produced at epithelial and immune barriers and is widely reviewed as a multifunctional antimicrobial and immune-modulating peptide. [1][3]
The molecule matters because it sits at the interface of microbes, skin and mucosal barriers, neutrophils, epithelial cells, and inflammatory signaling. That makes it relevant to wound, infection, rosacea, sepsis-biomarker, vitamin D, and immune-defense literature. [2][4][6]
LL-37 is not the same as the full hCAP18 precursor. The name refers to the mature 37-amino-acid peptide generated from human cathelicidin, while cathelicidin or hCAP18 can describe the broader precursor system. That naming distinction matters when comparing biomarker studies, topical formulations, and peptide products. [1][4]
What LL-37 is investigated for
LL-37 evidence is grouped by practical use case and topical, injectable, and oral route context. Each use case separates confidence, human evidence, animal or mechanistic support, and the practical takeaway.
Antimicrobial defense
Topical, Injectable
Antimicrobial defense
Topical, Injectable
LL-37 is central to antimicrobial-defense biology; therapeutic claims need route-specific human trials and should not be generalized to chronic systemic injection. [1][2]
Skin and barrier inflammation
Topical
Skin and barrier inflammation
Topical
Wound healing
Topical
Wound healing
Topical
Topical wound healing is a legitimate LL-37 research area, but it remains adjunctive and should not replace standard wound care or infection management. [5][21][23]
Evidence snapshot
Overall confidence
LL-37 has deep endogenous cathelicidin biology but weaker exogenous treatment evidence. Route and context matter because antimicrobial, barrier, and inflammatory effects can diverge. [1][4][40]
Overall confidence is a page-level composite, not an average; it weighs evidence quality, route/molecule match, and practical limitations.
Human evidence
Published human literature is strongest as biomarker and disease-context evidence, with topical trial activity still early. It does not establish broad clinical efficacy for LL-37 products. [6][40]
Animal / preclinical
Preclinical literature supports antimicrobial, immune, wound, and barrier-response biology across models. Those models do not settle route-specific treatment effects. [2][3]
Mechanism support
Cathelicidin biology gives LL-37 a well-established innate-immunity mechanism. The practical caveat is that inflammatory effects can shift by tissue, dose, and disease context. [1][4]
Forms & administration
LL-37 administration splits into topical wound or skin research and injectable immune-support protocol conventions. These route contexts are not interchangeable. [40][4][36]
Dosing & protocols
The notes below separate published trial design from commonly discussed cosmetic or compounded-use patterns. They are educational context only, not a prescription or product instruction.
Typical Range
Common injectable range is 500 mcg-1.6 mg per dose. Topical products are formulation-specific and should not be converted from injectable amounts. [4][36]
Frequency
Common short-course injectable schedules use 1-2 daily touchpoints. Topical wound schedules follow the study product and wound-care plan. [40]
Timing Considerations
Morning or evening timing works for injectable consistency. Topical wound use aligns with dressing changes and clinician-directed wound care. [40]
Cycle Length
Injectable protocols are commonly short 2-4 week cycles. Wound and skin use is reassessed by healing, irritation, and infection markers. [40]
What to expect
First week
Topical wound or skin use may first show changes in redness, drainage, pain, surface irritation, or barrier comfort. [40]
Weeks 2-4
Wound size, barrier comfort, flare frequency, and pain are the clearest short-course patterns for topical use; injectable immune-support expectations remain much less concrete. [40][4]
After stopping
Barrier comfort and wound trajectory may hold, fade, or return toward baseline depending on wound care and other skin-care changes. [40]
Safety profile
Topical LL-37 safety centers on local irritation and wound-care context. Injectable or systemic exposure is a different risk category, with added immune-activation, sterility, product-quality, and unknown exposure concerns. [40][36][39]
Who LL-37 is not for
Route-specific avoid and medical-review notes:
Drug & supplement interactions
Documented interactions are separated from theoretical or route-specific cautions.
Theoretical interactions
- Immunosuppressive therapy
Immunosuppressive therapy could change infection and inflammation context for topical or injectable LL-37; this is a theoretical route-specific immune caution. [2]
Regulatory status
United States
LL-37 has no FDA-approved topical or injectable drug use as of 2026-06-21. FDA's compounding materials flag cathelicidin LL-37 in a withdrawn Category 2 safety-risk context, so research-market availability should not be read as a cleared human-use product. [36][38][39]
| Route | FDA drug approval | 503A compounding |
|---|---|---|
| Topical | Not Approved As of 2026-06-21, LL-37 was not FDA-approved as a topical wound drug or injectable/systemic drug. Topical trial activity and research-market products do not create FDA approval. [36][39] | Flagged FDA lists cathelicidin LL-37 among nominated bulk substances withdrawn after Category 2 safety-risk concerns; that compounding context is separate from topical research and does not approve compounded LL-37. [38][39] |
| Injectable | Not Approved As of 2026-06-21, LL-37 was not FDA-approved as a topical wound drug or injectable/systemic drug. Topical trial activity and research-market products do not create FDA approval. [36][39] | Flagged FDA lists cathelicidin LL-37 among nominated bulk substances withdrawn after Category 2 safety-risk concerns; that compounding context is separate from topical research and does not approve compounded LL-37. [38][39] |
Topical
Injectable
International
EU/Europe, UK, Canada, and Australia should be checked by local product and claim; topical research activity does not equal therapeutic market authorization.
Sports & competition
WADA's 2026 Prohibited List does not specifically name LL-37, but tested athletes should treat systemic use of a non-approved pharmacological substance as an S0 risk unless cleared through anti-doping review. [41]
How it works
LL-37 is the active human cathelicidin peptide at barrier surfaces. It can damage microbes directly, but its broader role is signaling: recruiting immune cells, changing inflammatory tone, and influencing epithelial and wound-response behavior. [1][2][3]
That dual action is why route matters. Topical LL-37 logic is tied to local skin or wound exposure, while injectable or systemic use would expose immune-active pathways more broadly. Endogenous host-defense biology should not be read as proof that added LL-37 improves immunity or healing in people. [4][22][40]
Research gaps & open questions
What the current literature has not yet settled about LL-37:
Published topical LL-37 wound outcomes would help separate plausible barrier biology from clinical utility. [40]
Injectable pharmacokinetics, immune activation, and long-term safety need direct human study. [36][4]
Disease-specific inflammatory contexts need to be separated because LL-37 can participate in both defense and inflammatory signaling. [2]
Common questions
What is LL-37?
Is LL-37 an antibiotic?
Myths & misconceptions
Myth
Because LL-37 is natural, exogenous LL-37 is automatically safe.
Myth
LL-37 is a simple immune booster.
Reality
LL-37 is immune-active and context-dependent, which is different from a predictable immune boost. [2]
History & discovery
LL-37's history starts in human cathelicidin biology: hCAP18 processing produces a 37-amino-acid peptide that became a model for barrier defense, immune signaling, and wound biology. [1][2]
Reviews established LL-37 as the mature active peptide from hCAP18, the only human cathelicidin, distinguishing it from conventional antibiotics or generic antimicrobial products. [1][3]
Research expanded from direct antimicrobial activity into chemotaxis, epithelial activation, angiogenesis, inflammation control, and other host-defense functions. [2][3]
Topical LL-37 cream moved into diabetic-foot-ulcer testing, a route-specific therapeutic question separate from injectable compounding discussions. [40]
41 studies
LL-37, the only human member of the cathelicidin family of antimicrobial peptides.
Biochimica et biophysica acta, 2006 Sep. review.
The roles of cathelicidin LL-37 in immune defences and novel clinical applications.
Current opinion in hematology, 2009 Jan. review.
Cathelicidin LL-37: a multitask antimicrobial peptide.
Archivum immunologiae et therapiae experimentalis, 2010 Feb. review.
A comprehensive summary of LL-37, the factotum human cathelicidin peptide.
Cellular immunology, 2012 Nov. review.
Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial.
Wound repair and regeneration : official publication of the Wound Healing Society [and] the European Tissue Repair Society, 2014 Sep-Oct. human clinical.
Effect of Cholecalciferol Supplementation on Vitamin D Status and Cathelicidin Levels in Sepsis: A Randomized, Placebo-Controlled Trial.
Critical care medicine, 2015 Sep. human clinical.
Significant Effects of Oral Phenylbutyrate and Vitamin D3 Adjunctive Therapy in Pulmonary Tuberculosis: A Randomized Controlled Trial.
PloS one, 2015. human clinical.
Nasal Levels of Antimicrobial Peptides in Allergic Asthma Patients and Healthy Controls: Differences and Effect of a Short 1,25(OH)2 Vitamin D3 Treatment.
PloS one, 2015. human clinical.
Cow's milk and rice fermented with Lactobacillus paracasei CBA L74 prevent infectious diseases in children: A randomized controlled trial.
Clinical nutrition (Edinburgh, Scotland), 2017 Feb. human clinical.
Impact of high-dose vitamin D(3) on plasma free 25-hydroxyvitamin D concentrations and antimicrobial peptides in critically ill mechanically ventilated adults.
Nutrition (Burbank, Los Angeles County, Calif.), 2017 Jun. human clinical.
Serum level of cathelicidin LL-37 in patients with active tuberculosis and other infectious diseases.
Journal of biological regulators and homeostatic agents, 2017 Jul-Sep. human clinical.
Reduction of respiratory infections in asthma patients supplemented with vitamin D is related to increased serum IL-10 and IFNγ levels and cathelicidin expression.
Cytokine, 2018 Aug. human clinical.
Vitamin D and Phenylbutyrate Supplementation Does Not Modulate Gut Derived Immune Activation in HIV-1.
Nutrients, 2019 Jul 21. human clinical.
The therapeutic efficacy of Bifidobacterium animalis subsp. lactis BB-12(®) in infant colic: A randomised, double blind, placebo-controlled trial.
Alimentary pharmacology & therapeutics, 2020 Jan. human clinical.
Therapeutic Potential of Cathelicidin Peptide LL-37, an Antimicrobial Agent, in a Murine Sepsis Model.
International journal of molecular sciences, 2020 Aug 19. review.
Seasonal Antimicrobial Activity of the Airway: Post-Hoc Analysis of a Randomized Placebo-Controlled Double-Blind Trial.
Nutrients, 2020 Aug 27. human clinical.
A randomized controlled trial on the coloprotective effect of coenzyme Q10 on immune-inflammatory cytokines, oxidative status, antimicrobial peptides, and microRNA-146a expression in patients with mild-to-moderate ulcerative colitis.
European journal of nutrition, 2021 Sep. human clinical.
Dose effect of bovine lactoferrin fortification on diarrhea and respiratory tract infections in weaned infants with anemia: A randomized, controlled trial.
Nutrition (Burbank, Los Angeles County, Calif.), 2021 Oct. human clinical.
Impact of vitamin D status and cathelicidin antimicrobial peptide on adults with active pulmonary TB globally: A systematic review and meta-analysis.
PloS one, 2021. review.
Functional Antibodies and Innate Immune Responses to WRSS1, a Live Oral Shigella sonnei Vaccine Candidate, in Bangladeshi Adults and Children.
The Journal of infectious diseases, 2021 Dec 20. human clinical.
Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trial.
Wound repair and regeneration : official publication of the Wound Healing Society [and] the European Tissue Repair Society, 2021 Nov. human clinical.
Reduction of Erythema in Moderate-Severe Rosacea by a Low Molecular Weight Heparan Sulfate Analog (HSA).
Journal of drugs in dermatology : JDD, 2023 Jun 1. human clinical.
Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trial.
Archives of dermatological research, 2023 Nov. human clinical.
Efficacy and safety of Oral LL-37 against the Omicron BA.5.1.3 variant of SARS-COV-2: A randomized trial.
Journal of medical virology, 2023 Aug. human clinical.
Effect of weekly vitamin D supplementation on the severity of atopic dermatitis and type 2 immunity biomarkers in children: A randomized controlled trial.
Journal of the European Academy of Dermatology and Venereology : JEADV, 2024 Sep. human clinical.
Outcomes of High-Dose Versus Low-Dose Vitamin D on Prognosis of Sepsis Requiring Mechanical Ventilation: A Randomized Controlled Trial.
Journal of intensive care medicine, 2024 Oct. human clinical.
Acute salivary antimicrobial peptide secretion response to different exercise intensities and durations.
American journal of physiology. Regulatory, integrative and comparative physiology, 2024 Dec 1. human clinical.
Weekly Vitamin D Supplementation to Prevent Acute Respiratory Infections in Young Children at Different Latitudes: A Randomized Controlled Trial.
The Journal of pediatrics, 2024 Dec. human clinical.
Associations between vitamin D status and biomarkers linked with inflammation in patients with asthma: a systematic review and meta-analysis of interventional and observational studies.
Respiratory research, 2024 Sep 19. review.
The Immunomodulatory Activity of High Doses of Vitamin D in Critical Care Patients with Severe SARS-CoV-2 Pneumonia-A Randomized Controlled Trial.
Nutrients, 2025 Jan 31. human clinical.
Acute effects of continuous and interval cycling on salivary SIgA and anti-microbial peptide secretions: a randomized crossover trial.
European journal of applied physiology, 2026 Feb. human clinical.
Limosilactobacillus fermentum LF61: A multidimensional study on safety and functionality from genomics to clinical application.
Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association, 2026 May. human clinical.
Cancer cell migration under control of human cathelicidin LL-37.
Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie, 2026 May. review.
LL-37-ApoB-100 Complex Serves as a Biomarker of Coronary Artery Disease.
Arteriosclerosis, thrombosis, and vascular biology, 2026 Jun. human clinical.
Role of Bruton's Tyrosine Kinase in mast cell driven urothelial barrier injury in an LL-37 induced model of interstitial cystitis.
Scientific reports, 2026 Apr 30. in vitro.
Drugs@FDA/openFDA query for LL-37
U.S. Food and Drug Administration / openFDA. database query.
Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act
U.S. Food and Drug Administration, 2026-05-14. regulatory.
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks
U.S. Food and Drug Administration, 2026-05. regulatory.
Compounding and the FDA: Questions and Answers
U.S. Food and Drug Administration. official guidance.
Efficacy of LL-37 Cream on Bacteria Colonization, Inflammation Response and Healing Rate of Diabetic Foot Ulcers
ClinicalTrials.gov. clinical trial registry.
The 2026 List of Prohibited Substances and Methods
World Anti-Doping Agency, 2026. regulatory.