Researchers found that the antimicrobial peptide LL-37, part of the cathelicidin family, is naturally produced in human sweat and helps kill a wide range of bacteria. This adds to the known skin defense provided by another peptide called dermcidin.

The eccrine gland is one of the major cutaneous appendages and secretes sweat. Its principal function is thermoregulation during exposure to a hot environment or physical exercise. In addition to this function, we show that LL-37, a member of cathelicidin family of anti-microbial peptides, is expressed in sweat. LL-37 protein and mRNA was seen in the eccrine structures of normal human skin by immunohistochemistry and in situ hybridization. LL-37 was localized to both the eccrine gland and sweat ductal epithelial cells, whereas dermcidin, a previously described natural antibiotic in sweat, was expressed only in the gland itself. The anti-microbial activity of LL-37 and dermcidin against various bacteria in the sweat ionic environment was demonstrated by solution colony forming assay using synthetic peptides, and in sweat obtained from normal volunteers. These results indicate that cathelicidin is secreted in human sweat, has potent anti-microbial activity against both gram-positive and gram-negative bacteria, and can, after processing from the preproform, provide a barrier for protection against infection. Thus, sweat represents a unique mode of delivery for potent innate immune effector molecules in the absence of inflammation.