How do microbes on the skin aid in innate immunity?

Microbes on the skin contribute significantly to innate immunity primarily through the production of fatty acids that inhibit pathogens. The skin hosts a diverse microbiota, which includes various beneficial bacteria. These bacteria metabolize lipids present on the skin’s surface, resulting in the production of fatty acids, like lactic acid and propionic acid. These fatty acids play a crucial role in maintaining the skin's acidic environment, which helps to inhibit the growth of pathogenic organisms that may cause infections.

Additionally, the lower pH created by these fatty acids is not conducive to the survival of many harmful microbes, thereby providing a barrier against infections. This process helps to create a balanced ecosystem on the skin, where beneficial bacteria can thrive while limiting the presence and growth of potentially harmful pathogens. This function underscores the important role of the skin microbiota in the body's first line of defense against external microbial threats.