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LL-37

Last reviewed: April 18, 2026 by The Peptide Catalog Team

An antimicrobial peptide for immune defense and wound healing. LL-37 is a human cathelicidin antimicrobial peptide that plays a role in innate immunity. Studied for its antimicrobial, immunomodulatory, and wound healing properties. Researched in contexts of infection, inflammation, and immune support.

CategoryHealing & Recovery Peptides
Classimmune modulator
GoalGut HealthImmune Support
Overview

Core Benefits

Key Advantages
Antimicrobial defense
Kills bacteria, viruses, and fungi by disrupting membranes.
Biofilm disruption
Breaks down biofilms that shield bacteria from antibiotics.
Innate immunity boost
Recruits and activates immune cells at infection sites.
Wound healing support
Promotes angiogenesis and tissue repair during healing.
Vitamin D connection
Vitamin D upregulates endogenous LL-37 production.
Natural human peptide
Body's own cathelicidin — produced in immune cells and skin.

These are educational summaries of commonly discussed effects in wellness/regenerative contexts, not guarantees.

LL-37 Results Timeline

Progression
1
Week 1–2
Physical Changes
Initial inflammatory response modulation, early tissue repair signals
Performance & Recovery
May notice reduced discomfort at injury sites
Other Benefits
Improved gut comfort (if applicable), better sleep quality
2
Week 3–4
Physical Changes
Visible improvement in healing tissues, reduced swelling
Performance & Recovery
Increased mobility and flexibility in affected areas
Other Benefits
Enhanced recovery from workouts, improved overall well-being
3
Month 2–3
Physical Changes
Significant tissue repair progress, improved joint comfort
Performance & Recovery
Return to normal activity levels, reduced pain
Other Benefits
Systemic healing benefits, improved skin quality
4
3+ Months
Physical Changes
Near-complete healing of targeted tissues
Performance & Recovery
Full functional recovery in many cases
Other Benefits
Cumulative benefits build over multiple 8-week on/off cycles; many see best results with 2-3 cycles

Timeline is illustrative and non-guaranteed. Outcomes vary and are commonly discussed alongside training, nutrition, sleep, and cycling practices.

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Evidence at a glance

Two parallel grades per outcome — clinical RCT depth and real-world community adoption. See the Research Overview below for citations and detail.

OutcomeClinical EvidenceCommunity Evidence
Wound healing / re-epithelializationWeakWeak
Antimicrobial activity (broad-spectrum)ModerateWeak
Chronic wound closure (clinical)PreliminaryWeak
Pro-inflammatory effects in rosaceaModerateWeak
How It WorksAntimicrobial Peptide — Human Cathelicidin

Target → Membrane Disruption → Immune Defense → Outcomes

1
Target

Microbial Membranes + Immune Cell Recruitment

LL-37 is the only human cathelicidin — an endogenous antimicrobial peptide your body naturally produces. It directly disrupts bacterial, viral, and fungal membranes while simultaneously recruiting and activating immune cells.

2
Cellular Signal

Membrane Disruption + Chemokine Release + Biofilm Attack

LL-37 inserts into microbial membranes, creating pores that kill pathogens. It also triggers chemokine release to recruit immune cells, modulates inflammatory responses, and disrupts bacterial biofilms — protective structures that make infections resistant to antibiotics.

3
Systemic Effect

Broad-Spectrum Antimicrobial + Immune Modulation

Direct killing of bacteria, viruses, and fungi. Biofilm disruption makes resistant infections more vulnerable. Immune cell activation enhances the body's own defense response. Also promotes wound healing through angiogenesis stimulation.

4
What You Notice

Immune Support → Infection Resolution → Wound Healing

Often used during acute infections or for immune support protocols. May help resolve stubborn or biofilm-protected infections. Supports wound healing. Vitamin D increases natural LL-37 production — part of why vitamin D supports immune health.

What Makes This Peptide Different

LL-37 is the only human cathelicidin— your body already makes it. Unlike synthetic antimicrobials, it works through multiple mechanisms simultaneously (membrane disruption, biofilm attack, immune recruitment, wound healing). Its connection to vitamin D is notable — vitamin D upregulates LL-37 expression, which is part of vitamin D's immune-supporting mechanism.

Research overview

Outcome-by-outcome look at what the evidence actually supports for LL-37, including human vs. animal study counts and our editorial take on each.

Wound healing / re-epithelialization

Clinical:WeakCommunity:Weak

Heilborn 2003 showed that LL-37 expression is upregulated at the leading edge of healing acute wounds but absent in chronic ulcer epithelium, suggesting endogenous deficit drives non-healing. Carretero 2008 demonstrated that recombinant LL-37 transferred via adenovirus accelerated re-epithelialization in ob/ob diabetic mice. A Phase 2 venous ulcer trial of synthetic LL-37 was reported but cleanly indexing the primary publication remains a verification challenge.

1 human study · 6 animal studies

Key findings & citations
  • LL-37 strongly expressed at acute wound edges; absent in chronic ulcer epithelium.
  • Adenoviral LL-37 transfer accelerated re-epithelialization in diabetic mouse wounds.
  • Phase 2 venous leg ulcer trial of synthetic LL-37 reported clinical benefit at intermediate doses.

Our take

Mechanism is solid, the clinical trial program never reached approval. Reasonable as adjunct in non-healing wounds where standard care fails, but data is thin.

Antimicrobial activity

Clinical:ModerateCommunity:Weak

LL-37 has well-characterized broad-spectrum antimicrobial activity against bacteria, fungi, and some viruses via membrane disruption. Vandamme 2012 reviews the in vitro activity comprehensively. Translation to human infection treatment has been hindered by serum protein binding and salt sensitivity reducing in vivo potency.

0 human studies · 4 animal studies

Key findings & citations
  • Broad-spectrum activity vs Gram-positive, Gram-negative, fungi, biofilms in vitro.
  • Membrane-disrupting mechanism reduces resistance evolution risk.
  • Activity is salt- and serum-sensitive — limits systemic therapeutic potential.

Our take

Genuinely interesting antimicrobial pharmacology, but topical use only is realistic. Don't expect injectable LL-37 to act like an antibiotic.

Inflammatory skin disease (rosacea)

Clinical:ModerateCommunity:Weak

This is the cautionary side. Yamasaki 2007 showed that abnormal LL-37 processing drives rosacea pathogenesis — facial skin in rosacea patients overexpresses LL-37 fragments that trigger inflammation and vascular changes. Subsequent NLRP3 inflammasome work confirmed the pro-inflammatory mechanism.

2 human studies · 5 animal studies

Key findings & citations
  • Rosacea facial skin contains abnormally elevated cathelicidin and KLK5.
  • LL-37 fragments activate the NLRP3 inflammasome in keratinocytes.
  • Treatments that work for rosacea (azelaic acid, ivermectin) reduce LL-37 / KLK5 expression.

Our take

If you have rosacea-prone skin, exogenous LL-37 is exactly the wrong move. The peptide that helps a chronic ulcer can drive a flush.

What LL-37 doesn't do

Claims that current evidence does not support. Worth knowing before you set expectations.

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Dosing ProtocolImmunity / Antimicrobial

Educational reference only. Individual responses vary. Consult healthcare provider before use.

Vial Size
5 mg
Reconstitution
2 ml BAC water
Dose
125 mcg (5 units on 1ml syringe)
Timing
AM
Frequency
Daily
Duration
50 days straight, then 4 weeks off
Protocol Notes
Human antimicrobial peptide. Often used during acute infections or for immune support protocols.

Why This Dosing Protocol

Why 50 days straight? Antimicrobial protocols require sustained levels to fully resolve infections, especially biofilm-protected ones. The extended daily dosing ensures consistent antimicrobial pressure.

Why 4 weeks off after? Allows the immune system to recalibrate after the intensive antimicrobial protocol. LL-37 modulates immune responses — cycling prevents potential immune overactivation.
Full Dosing GuideReconstitution CalculatorCycle Cost Calculator

Reconstitution Calculator

Dilution math and unit conversions. Prefilled using a common vial size for this peptide.

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Storage & Handling

Storage at a glance

Proper storage temperatures, shelf life, reconstitution best practices, and travel tips for lyophilized and reconstituted peptides.

Powder: Freezer
1+ year at -20°C
Reconstituted: Fridge
4 weeks max at 2-8°C
View Complete Storage Guide

Handling specifics

Educational overview on storage, labeling, and traceability considerations for lab environments. Consult primary literature and vendor documentation for specifics.

Powder storage (very stable)
  • Freezer (-20°C): 1+ year
  • Refrigerator (2-8°C): 1-3 months
  • Room temperature: 2-3 weeks (emergency only)
Reconstituted storage (fragile)
  • MUST refrigerate at 2-8°C
  • 4-week maximum shelf life
  • NEVER freeze after reconstitution
  • Use bacteriostatic water for multi-dose
Molecular Structure

LL-37 sequence

Click any residue to see its properties.

HydrophobicPolarAcidic (−)Basic (+)Special

Sequence-derived properties

Length
37 residues
Molecular weight
4493.3 Da
backbone only
Avg hydrophobicity
-0.72
Kyte–Doolittle scale

Residue classes

Hydrophobic: 13 (35%)Polar: 5 (14%)Acidic (−): 5 (14%)Basic (+): 11 (30%)Special: 3 (8%)

Net charge distribution

Positive11 (30%)
Neutral21 (57%)
Negative5 (14%)

Amino acid frequency

K×6R×5F×4L×4E×3I×3D×2G×2S×2V×2

Modifications

  • Cathelicidin-derived antimicrobial peptide

Sequence and properties provided for educational reference. Not for clinical dosing decisions.

  • Length: 37 amino acids
    (Derived from hCAP18.)
  • Structure: α-helical
    (Amphipathic membrane-active.)
  • Mechanism: Membrane disruption
    (Direct antimicrobial + immune modulation.)
  • Primary Use: Immune support
    (Antimicrobial + wound healing.)
N-terminal sequence
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES
LL-37 disrupts microbial membranes while also modulating immune responses, promoting wound healing, and exhibiting anti-biofilm activity. Vitamin D increases its expression.
Key takeaway: LL-37 is a natural antimicrobial with dual direct-killing and immune-modulating effects. Research interest in infections, wound healing, and immune regulation.

FAQ

What is LL-37?

LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid peptide that plays a crucial role in innate immunity. It has broad-spectrum antimicrobial activity against bacteria, viruses, and fungi, plus immunomodulatory properties. Produced naturally by immune cells, skin, and mucosal tissues.

How does LL-37 kill pathogens?

LL-37 kills microbes primarily by disrupting their cell membranes. Its positive charge attracts it to negatively charged bacterial membranes, where it inserts and creates pores, causing cell death. It also neutralizes bacterial toxins (like LPS) and can disrupt viral envelopes. Human cells are protected because their membranes have a different composition.

What is LL-37's anti-biofilm activity?

Biofilms are protective structures bacteria create that make them resistant to antibiotics. LL-37 can penetrate and disrupt biofilms, making the bacteria vulnerable again. This is particularly relevant for chronic infections like those in wounds, implants, or the lungs in cystic fibrosis patients.

What is the connection between Vitamin D and LL-37?

Vitamin D directly upregulates LL-37 production — this is a major mechanism behind vitamin D's immune benefits. When vitamin D binds its receptor, it activates the gene for LL-37. This explains why vitamin D deficiency is linked to increased infection susceptibility. Sun exposure and vitamin D supplementation both increase LL-37 levels.

What conditions is LL-37 being researched for?

Research areas include chronic wounds, diabetic ulcers, bacterial infections (including antibiotic-resistant strains), viral infections, cystic fibrosis lung infections, periodontal disease, and as a potential cancer therapy due to effects on tumor cells. It's also studied for inflammatory conditions due to its immune-modulating properties.

What are the side effects of LL-37?

As a naturally occurring human peptide, LL-37 is generally well-tolerated. Potential side effects may include injection site reactions (pain, redness) and rarely mild flu-like symptoms. High concentrations can be cytotoxic, so proper dosing is important. Most research uses low doses that are well-tolerated.

How long does reconstituted peptide last?

Once mixed with bacteriostatic water, peptides remain stable for up to 4 weeks when refrigerated at 2-8°C (36-46°F). Unopened powder can last 1+ year in the freezer. Get our complete Storage & Travel Guide.

Is this peptide legal to purchase?

Peptides sold "for research purposes only" are legal to purchase in the US, but are not FDA-approved for human use outside of specific medical applications. Always consult a healthcare provider before use.

New to peptides?

Take our Peptide Match tool to find the best peptide for your goals. You can also read our Complete Guide to Peptides to learn the basics.

Scientific Sources

The following peer-reviewed studies and official resources provide additional scientific context for this peptide:

LL-37 Research Articles

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LL-37 Dosage Chart: 125mcg/Day for 50 Days

Most protocols miss the vitamin D co-factor that activates LL-37. Covers 125mcg daily, 50-day cycling, and TA-1 stacking.

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LL-37 Benefits: Biofilm Breaker + 9 Immune Effects

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Buy LL-37: Compare 3 Vendors, From $45

Compare 3 LL-37 vendors side by side: from $45 a vial, best value $7.80/mg. Codes save up to 50%. Vial sizes, COA status, real cost per week.

results

LL-37 Results Timeline: Week-by-Week

Acute users describe shifts in 1-2 weeks; CIRS protocols run months. Full LL-37 timeline by use case, with biomarker watch and variability factors.

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Disclosure: we may earn affiliate commission from qualifying purchases. Educational information only — not medical advice.