Overview: What are warts?
The CPSA gratefully acknowledges Jessica Ho, MSc Public Health, MD candidate, Queen’s University, and Yuka Asai, MD, PhD for assistance in the preparation of this report. August 2021.
Warts are small growths on the skin caused by the human papillomavirus (HPV). This virus invades skin cells and enters a resting period, called latency, that may last for months or years. During latency, the virus multiplies and invades additional cells, which then take on the appearance of warts. Over 200 strains of HPV have been identified from DNA sequence data,1 more information on HPV can be found here (link to HPV section). Certain strains tend to infect specific areas of the skin and there are six primary types of warts.
Primary types of warts:
- Filiform (warts that have long, narrow strands that extend about 1 to 2 millimeters from the skin)
- Periungual (located around a nail)
Warts are contagious and can spread through direct and indirect contact. This includes direct spread via skin to skin contact as well as indirectly from surfaces (fomites). All warts are more likely to spread by trauma to the skin which may occur through nail-biting, picking of the wart, rubbing (such as via callouses) and activities like shaving. Genital warts may be spread through skin to skin contact that occurs with sexual activity. Fomites are objects or surfaces that can spread infections like HPV. Spread via fomites may occur on contact with surfaces such as shower stall floors, swimming pool decks and improperly cleaned instruments that have been in contact with an HPV infection. Oral warts may also occur and can be seen in uncommon conditions such as focal epithelial hyperplasia (Heck’s disease).
Some people may have a predisposition to HPV infection and the development of warts. Often these are people who have immunodeficiencies where the body is more susceptible to infections such as HPV. While these are rare, immunodeficiencies include conditions like epidermodysplasia verruciformis (EDV).
Although warts frequently recur after treatment, many will disappear spontaneously within two to three years. Some strains of HPV that cause genital warts have the potential to cause cancer of the cervix, vulva, penis and anus. More information about the development of cancer related to HPV infections can be found in the HPV section (link to HPV section).
- Approximately 7 to 12 percent of the general population is affected by warts.
- Both men and women are equally affected by warts. Up to 50 percent of all men and women have been infected by HPV at some point in their lives.
- Warts are common in children. Approximately 10 to 20 percent of school-aged children are affected.
- In children, the incidence of warts peaks at 12 to 16 years of age.
- Warts are twice as frequent in those that identify as White compared to those of African or Asian descent.
- Approximately 65 percent of non-genital warts disappear without treatment within two to three years.
- Genital warts are considered the most common sexually transmitted disease, affecting approximately 1 percent of the population.
- Genital warts are most common in individuals aged 17 to 33 years of age.
- It is estimated that 75 percent of sexually active men and women will experience at least one genital HPV infection in their life.