Palmar (hand) warts. View of two warts (verrucas) seen on the palm of a hand. Warts are contagious, but harmless, caused by the human papilloma virus (HPV), of which there are at least thirty different types. Infection is common and affects only the outermost layer of skin giving warts a firm, sharply defined appearance. They may appear in a range of colours and textures from smooth to irregular. Fifty percent of all warts will disappear spontaneously within a year. They can however be removed by chemicals, by freezing (cryotherapy), by scraping (curettage), by burning (cautery), or by laser treatment.