Docosanol is a naturally-occurring 22-carbon saturated aliphatic alcohol. The drug has in vitro activity against various Herpesviridae, including herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), cytomegalovirus (CMV), respiratory syncytial virus (RSV), varicella zoster virus (VZV), and human immunodeficiency virus type 1 (HIV-1). The mechanism of action of docosanol in the treatment of herpes labialis lesions does not involve direct virucidal activity against HSV. The drug appears to interfere with fusion of the HSV envelope and host cell membranes, thereby preventing HSV entry into host cells and subsequent viral replication.