Antimicrobial peptides are produced by plants and most organisms throughout the animal kingdom including humans. Antimicrobial peptides protect against a broad range of infectious agents, as bacteria, fungi, and viruses. The amphibian skin is an especially rich source of antimicrobial peptides. See also the product families: Hepcidins LL-37 and Fragments Tuftsin and Analogs (subfamily).

Defensins comprise a family of small, cationic peptides prevalent in neutrophil granulocytes of humans, rabbits, guinea pigs and rats as well as in rabbit lung macrophages. These peptides show sequence homology and contain 6 conserved disulfide-linked cysteines. In vitro, all defensins display a range of prominent antimicrobial activities against bacteria, fungi, and certain enveloped viruses. In addition, human and rabbit defensins exert potent cytotoxicity in vitro against various mammalian tumor cells. The defensins act on their targets by permeabilizing the plasma membranes.

β-Defensin 1 (BD-1) (human) is a small cationic peptide originally isolated from human plasma. It exerts antimicrobial activity and is constitutively expressed in epithelia at the mucosal surface. A role for BD-1 in innate immune response has been proposed.