Warts are small lumps that develop on the skin, either singularly or in clusters. Commonly occurring on the hands and feet, warts are non-cancerous and non-harmful, but can be embarrassing and unsightly. Warts are caused by an infection of the human papilloma virus, or HPV. This causes an excess of keratin, a hard protein that occurs naturally in the skin, resulting in the appearance of warts. The infection can be transmitted skin to skin contact, or contact with contaminated surfaces.