Papillomavirus particles. Coloured transmission electron micrograph (TEM) of a para-crystalline array of particles (green and red) of the human papillomavirus (HPV). The regular arrangement of these particles is like that seen for the atoms of a crystal. HPV is the cause of warts, growths that are commonly found on the hands, the soles of the feet, the body's mucous membranes and also on the genitals. HPV has also been linked with some skin and cervical cancers.