A callus is a thickened area of skin on the foot caused by pressure and repeated rubbing, such as from a shoe or sock. The rubbing causes the skin to produce a layer of protective skin (a callus). Calluses vary in size, and can become painful. There are a number of treatments for painful calluses.

A black, purple, or brownish discoloration under or involving a toenail is frequently due to trauma to the toe nail, such as when something is dropped on the toe. The color results from a blood clot or bleeding under the nail, and may involve the entire nail or just a small portion of it. This can be

Athlete's foot is a skin infection caused by fungus. A fungal infection may occur on any part of the body; on the foot it is called athlete’s foot, or tinea pedis.  Fungus commonly attacks the feet because it thrives in a dark, moist, warm environment such as a shoe. Fungal infections are more common