The human peptide LL‑37 can kill common skin‑fungi that cause athlete's foot, ringworm and yeast‑type rashes at low micromolar levels, and skin naturally makes more of it when infected. This suggests LL‑37 helps protect skin, but the study only tested it in the lab, not in real‑world products.

This study was designed to characterize the role of the human cathelicidin LL-37 in fungal skin infections such as dermatophytosis and tinea versicolor. The in vitro antimicrobial activity of synthetic antimicrobial peptides including the human cathelicidin LL-37 against Malassezia furfur and several dermatophytes was determined. Immunostaining was performed to determine expression of cathelicidin in skin biopsies from patients with tinea pedis, tinea corporis and tinea versicolor. Cathelicidin peptide expression was evaluated by western blotting and mRNA expression was studied in keratinocytes exposed to M. furfur or Trichophyton rubrum. LL-37 inhibits the growth of fungi with an MIC of 20-30 microM for M. furfur and 12.5 microM for Trichophyton mentagrophytes and T. rubrum. LL-37 also shows fungicidal activity with a minimum fungicidal concentration (MFC) of 12.5 and 25 microM for T. mentagrophytes and T. rubrum, respectively. An increase in cathelicidin expression was observed in human skin tissue infected with fungi compared with healthy skin. Western blotting of skin scrapings demonstrated that human cathelicidin is processed from its precursor into an active peptide in both healthy and infected plantar skin. These findings support a hypothesis that antimicrobial peptides such as cathelicidins can play a role in skin defence against dermatophytes and M. furfur.