All warts are infections caused by the human papilloma virus (HPV). There are over 100 varieties of HPV, from the highly contagious kind that causes genital warts, to the much less contagious kind that causes common warts on the hands and fingers. When this pesky virus invades this outer layer of our skin, usually through a cut or scratch, it causes rapid growth of cells on the outer layer of skin – which is what we call a wart.