center; usually only found on pressure points on the soles of the feet. Mosaic wart, a group of tightly clustered plantar-type warts, commonly on the hands or soles of the feet. Cause Warts are caused by the human papilloma virus (HPV). There are about 130 known types of human papilloma viruses. HPV infects the squamous epithelium, usually of the skin or genitals, but each HPV type is typically only able to infect a few specific areas on the body. Many HPV types can produce a benign growth, often called a "wart" or "papilloma", in the area they infect. Many of the more common HPV and wart types are listed below. Common warts – HPV types 2 and 4 (most common); also types 1, 3, 26, 29, and 57 and others. Cancers and genital dysplasia – "high-risk" HPV types are associated with cancers, notably cervical cancer, and can also cause some vulvar, vaginal, penile, anal and some oropharyngeal cancers. "Low-risk" types are associated with warts or other conditions. High-risk: 16, 18 (cause the most cervical cancer); also 31, 33, 35, 39, 45, 52, 58, 59, and others. Plantar warts (verruca) – HPV type 1 (most common); also types 2, 3, 4, 27, 28, and 58 and others. Anogenital warts (condylomata acuminata or venereal warts) – HPV types 6 and 11 (most common); also types 42, 44 and others. Low-risk: 6, 11 (most common); also 13, 44, 40, 43, 42, 54, 61, 72, 81, 89, and others. Verruca plana (flat warts) – HPV types 3, 10, and 28. Butcher's warts – HPV type 7. Heck's disease (focal epithelial hyperplasia) – HPV types 13 and 32. Pathophysiology Common warts have a characteristic appearance under the microscope. They have thickening of the stratum corneum (hyperkeratosis), thickening of the stratum spinosum (acanthosis), thickening of the stratum granulosum, rete ridge elongation, and large blood vessels at the dermoepidermal junction. Diagnosis On dermatoscopic examination, warts will commonly have fingerlike or knoblike extensions. Prevention Gardasil 6 is an HPV vaccine aimed at preventing cervical cancers and genital warts. Gardasil is designed to prevent infection with HPV types 16, 18, 6, and 11. HPV types 16 and 18 currently cause about 70% of cervical cancer cases, and also cause some vulvar, vaginal, penile and anal cancers. HPV types 6 and 11 are responsible for 90% of documented cases of genital warts. Gardasil 9, approved in 2014 protects against HPV