Saliva, tears, and nasal mucus all contain an antimicrobial enzyme called lysozyme. This enzyme is part of our immune system, and protects us from foreign pathogens, such as bacteria, viruses, and fungi. Lysozyme is also present in human milk. Skin is the primary immune system protection against pathogens, and saliva, tears, and nasal mucus protect the paths into the body that skin can't protect.