Warts and verrucas – which affect one in ten adults and one in three children – are caused by the human papillomavirus (HPV). But what is human papillomavirus? HPV is a very common virus that infects the top layer of human skin or mucous membranes. Over 100 different strands of the virus have been identified and of these approximately 60 varieties cause warts on the hands and feet, as well as the face. These types of HPV are generally harmless. The rest are transmitted through sexual contact and can cause genital warts. Not all sexually transmitted HPV varieties are dangerous, but in some cases an infection can lead to cervical cancer. Since the virus can take many shapes and forms, it is important to get the facts about HPV.