LL37, Research peptide, Lyophilized powder, Antimicrobial activity, Skin repair, Anti-inflammatory, Host defense peptide, Wound healing

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LL37 is a naturally derived peptide with multiple biological activities, also classified as a host defense peptide. Thanks to its unique amino acid sequence, it demonstrates significant biological potential in areas such as antimicrobial action, anti-inflammation, and skin repair, making it a highly regarded active ingredient in skincare research and peptide-based product development. Named for the leucine residues at the termini of its amino acid sequence, LL37 is formed through the enzymatic processing of a precursor into an active, mature fragment. Widely present in various biological tissues, it operates via a multi-target mechanism—distinguishing it from traditional ingredients with single modes of action—and has become a popular choice for developing functional formulas and conducting *in vitro* model studies.

The defining characteristic of LL37 is its broad-spectrum antimicrobial activity. Unlike traditional antimicrobial ingredients that rely on a single mechanism, LL37 primarily inhibits the proliferation of harmful microorganisms—including bacteria and fungi—by disrupting their outer membrane structures and altering membrane permeability. Because its target is the microbial membrane structure, it is less likely to rapidly induce drug resistance compared to certain chemical antimicrobial agents; this is one of the most significant advantages of host defense peptide ingredients. In environments where microorganisms proliferate rapidly, LL37 inhibits the overgrowth of harmful flora, regulates the microbial balance, reduces the accumulation of harmful metabolites, and maintains micro-environmental stability. For the skin surface, which is prone to microbial imbalance, this peptide helps optimize the microbial community structure, mitigates irritation caused by the overgrowth of harmful microorganisms, alleviates discomfort resulting from microbial dysbiosis, and fosters a clean, stable environment for surface tissues.

In addition to its antimicrobial properties, LL37 possesses excellent anti-inflammatory regulatory capabilities. External stimuli can trigger a massive release of local inflammatory factors, leading to tissue redness and intensified stress responses, which in turn delay the self-repair process of surface tissues. LL37 modulates the expression of various inflammatory signaling molecules, downregulates the excessive release of pro-inflammatory factors, attenuates excessive stress responses, soothes local discomfort, and facilitates the micro-environment's smooth recovery from a state of stress. It does not completely block normal defense signals; instead, it modulates excessively amplified stress responses to a reasonable range, maintaining a balanced defense and preventing persistent low-grade inflammation from damaging surface tissues. This characteristic makes LL37 highly valuable for epidermal formulations frequently exposed to external irritants, as it simultaneously addresses the dual needs of antimicrobial action and soothing relief.

Regarding tissue repair, LL37 regulates cell migration and proliferation, accelerating the orderly migration of surface cells and facilitating the reconstruction of damaged epidermal structures. Orderly cell migration is crucial for wound closure when the epidermal barrier is compromised. By regulating the expression of relevant growth factors, LL37 guides cells toward the damaged area, accelerates surface tissue closure, promotes the synthesis of matrix components, and helps rebuild an intact barrier structure. Simultaneously, the peptide promotes the expression of vascular endothelial-related signals, optimizes local microcirculation, and enhances nutrient delivery efficiency; this provides ample nourishment for cell growth in the damaged area, further accelerating the repair process. In cases of fragile barriers or surface damage, sustained use gradually reinforces the barrier structure, improves surface resilience, and reduces recurrent damage caused by external irritants.

LL37 also offers additional benefits in matrix renewal and antioxidant protection. The continuous accumulation of environmental free radicals damages the extracellular matrix structure, accelerates tissue aging, and leads to issues such as roughness and a loss of radiance. LL37 boosts local antioxidant capacity, scavenges excess free radicals, mitigates matrix damage caused by oxidative stress, and protects extracellular components—such as collagen—from rapid degradation. Furthermore, it modulates fibroblast activity, promotes the production of extracellular matrix substances, and maintains the integrity of the matrix network. This improves conditions characterized by surface roughness, dryness, and a lack of smoothness, demonstrating significant potential for use in early anti-aging formulations.

As a research-grade peptide ingredient, LL37 possesses physicochemical properties well-suited for formulation development. Commercially available as a lyophilized powder, it exhibits excellent water solubility, allowing for uniform dispersion and dissolution in aqueous systems, making it compatible with various product formats such as serums, sprays, and repair lotions. This peptide maintains stable activity under appropriate storage conditions; by properly controlling the formulation's pH range, the rate of activity degradation can be effectively reduced, facilitating industrial production and long-term storage. It exhibits strong formulation compatibility and can be combined with moisturizing agents, plant extracts, and other reparative peptides to synergistically enhance skin barrier maintenance. During the compounding process, the overall system environment must be controlled to prevent direct contact with strong oxidizing agents, thereby avoiding damage to the peptide's spatial structure and a consequent loss of biological activity.

LL37 differs significantly from many common bioactive peptides. While most skincare peptides focus solely on promoting collagen synthesis or providing a single soothing effect, LL37 integrates multiple activities—including antimicrobial, anti-inflammatory, cell migration-promoting, and antioxidant properties—making it a multifunctional host defense peptide. In scenarios involving epidermal microbiome imbalance accompanied by barrier damage, conventional repair ingredients can replenish the matrix but fail to regulate harmful surface microorganisms, whereas traditional antimicrobial ingredients often lack reparative capabilities. LL37 can simultaneously address microbiome imbalance, stress-induced inflammation, and barrier disruption, achieving multidimensional, synergistic care; this is a key reason for the rising interest in this ingredient within the scientific community in recent years.

Extensive *in vitro* studies have confirmed that LL37’s biological activity is dose-dependent, delivering consistent efficacy within an optimal concentration range; however, excessive concentrations may pose a risk of irritation. Therefore, gradient concentration testing is essential during formulation development to determine the appropriate dosage while simultaneously assessing stability. In scientific research, LL37 is frequently used in experiments concerning host defense mechanisms, microbial resistance, and tissue repair, serving as a high-quality peptide source for basic research. In the cosmetics industry, an increasing number of formulators are incorporating it into barrier repair products, soothing serums, and topical wound-care formulations to address epidermal damage caused by various environmental factors.

Market demand for gentle, multi-effect reparative active ingredients continues to grow. Traditional high-potency antimicrobial ingredients tend to be irritating, while simple moisturizing ingredients cannot resolve inflammation or microbiome issues; naturally derived host defense peptides like LL37 effectively fill this market gap. Leveraging multiple mechanisms of action, it transcends single-function limitations to simultaneously modulate the skin microbiome, alleviate stress, and accelerate barrier reconstruction, thereby offering both immediate soothing and long-term barrier reinforcement. As research into peptides advances and our understanding of LL37’s pathways deepens, formulations are being optimized and application scopes expanded.

Overall, LL37 is a multifunctional host defense peptide that integrates broad-spectrum antimicrobial activity, inflammation modulation, promotion of cell migration, acceleration of tissue repair, and antioxidant effects. It maintains surface microbiome stability by disrupting microbial membrane structures, soothes local stress by regulating inflammatory signals, accelerates barrier reconstruction by guiding cell migration, and mitigates oxidative damage by scavenging free radicals. With excellent water solubility and formulation versatility, it is suitable for both *in vitro* research and the development of various repair and soothing products. Amidst the rapid evolution of peptide ingredients, LL37’s unique multi-target activity grants it an irreplaceable advantage in barrier repair and microbiome modulation. As further research findings are realized, it will continue to deliver significant value in skincare science and ingredient development, offering novel ingredient options and research avenues for the creation of multi-effect repair products.