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Warts or verruca, are hard, rough growths on the surface of the skin. Warts vary in size and shape and may appear anywhere on the body.
Causes
Warts result from infection by certain viruses called papillomaviruses. The viruses live in cells on the surface layer of the skin and do not infect the underlying tissue. The thickened surface layer forms folds into which little blood vessels grow spontaneously. If a wart is scratched open, the viruses may spread by contact to another part of the body or to another person.
Different types of warts
The common wart (verruca vulgaris) is a small, raised, rough lump on the skin made up of small columns of tissue arising from the base. Common warts vary in color from normal flesh tint to dark brown-black. They usually occur on the hands, elbows, knees, and less frequently on the face or eyelids. They may also appear around the edges of the nails.
Plantar warts (verrucae plantares) are the same as the common wart but are flattened by pressure because they appear on pressure-bearing areas. They may be painful because the nodule presses into the flesh.
Venereal or genital warts (condylomata acuminata) are a typical wart infection, usually transmitted by sexual contact. | 
