Warts are localized, superficial skin infections caused by human papillomaviruses or HPVs. The infection causes a reaction within the skin leading to a small superficial skin growth. More than 100 types of HPVs have been identified, and each type is associated with particular parts of the body.
Common Warts
Common warts, also known as verrucae vulgaris, are well-defined, dome-shaped growths with a rough surface. They are typically grayish brown and painless. Common warts frequently occur on the hands, although they might occur on any skin surface. Clusters of common warts can merge to form large areas of warty skin. "The Merck Manual for Healthcare Professionals" cites HPV types 1, 2, 4, 27 and 29 as frequent causal agents of common warts.
The American Academy of Dermatology points out that common warts frequently occur around the nails of people who bite their fingernails. These warts are termed subungual and periungual warts. Breaks in the skin caused by biting around the nails provide a point of entry for the causative HPVs. Warts around the nails can be more difficult to treat than warts in other locations.
Filiform Warts
Filiform warts are a variant of common warts. They differ in that several long, thin extensions grow out of the surface of the wart. Filiform warts most commonly occur on the face and neck, according to the University of Virginia Health System.
Plantar Warts
Plantar warts are known by the medical name verrucae plantaris. These warts typically occur on the soles of the feet, often on pressure points such as the heel or ball of the foot. Pressure from walking causes callus formation around the wart. Weight bearing generally causes pain in the affected area. Black dots toward the center of the warts represent tiny blood vessels, which bleed easily if the surface of the wart is scraped away. A cluster of plantar warts that merge is called a mosaic wart. "The Merck Manual for Healthcare Professionals" notes HPV type 1 is the most common cause of plantar warts.
Flat Warts
As the name implies, flat warts are only slightly raised above the skin surface. They are small, smooth, flat growths that tend to appear in clusters with many warts. The area around the mouth and the forehead are commonly affected. The lesions are yellowish, light brown or pink. Flat warts are painless. According to "The Merck Manual for Healthcare Professionals," HPV types 3, 10, 28 and 49 most often cause flat warts.
References
- Merck Manual: Warts
- American Family Physician: Cutaneous Warts--An Evidence-Based Approach to Therapy
- American Academy of Dermatology: Warts
- University of Virginia Health System: Warts
- "Principles and Practice of Infectious Diseases, Sixth Edition"; Gerald L. Mandell, M.D., et al, Editors; 2004
