A wart is a scaly excrescence on the skin caused by a virus which may arise without warning and disappear equally suddenly. They are caused by infection with the human papillomavirus. The papillomavirus invades the prickle cells and squamous cells that make up the outer layer of skin (epidermis), causing them to overmultiply. As the excells are pusheduptward, a visible lump forms on the surface of the skin. The tiny black dots that are sometimes seen on warts are small blood vessels.

Numerous remedies have been suggested but local freezing or cauterization are often effective. Verrucas are warts pushed into the soles of the feet by the weight of the body.