Many types of viruses invade the skin, but most medical concern focuses on only three groups. Warts are caused by the papillomavirus, and cold sores are caused by the herpes simplex virus, as is shingles. The third group of viruses that infect the skin is part of the poxvirus family. However, chickenpox remains a common childhood infection. A poxvirus also causes molluscum contagiosum.
Warts can develop at any age, but they are most common in children and least common in the elderly.
Although warts on the skin are easily spread from one area of the body to another, most are not very contagious from one person to another. Genital warts, however, are contagious. The overwhelming majority of warts are harmless. The most common types don't become cancerous. Only rare types and some that infect the uterine cervix and the penis very rarely become cancerous.