Papillomaviridae is an ancient taxonomic family of non-enveloped DNA viruses, collectively known as papillomaviruses. Several hundred species of papillomaviruses, traditionally referred to as "types", have been identified infecting all carefully inspected mammals, but also other amniotes such as birds, snakes and turtles. Infection by most papillomavirus types, depending on the type, is either asymptomatic (e.g. most Beta-PVs) or causes small benign tumors, known as papillomas or warts (e.g. human papillomavirus1, HPV6 or HPV11). Papillomas caused by some types, however, such as human papillomaviruses 16 and 18, carry a risk of becoming cancerous.