Plantar warts are small, rough, round growths that are medically known as verrucae and present on the bottom of the foot. They’re caused by a virus called the Human Papilloma Virus (HPV) in the outer skin layer and are often contracted in childhood. Once you’ve contracted the virus, you’ll always have it in your system, so plantar warts may pop up spontaneously throughout your lifetime. 

The HPV virus is spread through direct contact. If you have a break in the skin, like a small cut or graze, then you may contract the virus through sharing the same surface like a shower or a floor. Immune systems do respond differently and not everyone that comes in contact with the virus will develop plantar warts. Similarly, a weakened immune system may make you more susceptible. Because the virus thrives in warm, moist environments, it is often contracted in changing rooms, at public swimming pools and at gyms.