Plantar warts are a certain type of wart that occurs on the bottom of the feet or toes. Plantar warts are the result of HPV (human papillomavirus). The virus usually gets into small cuts or openings on the skin of the feet. These warts can cause pain and may spread to the surrounding skin if not treated. Plantar warts can grow very deep into the skin which makes them difficult to treat at home. The symptoms can include a hard spot of skin that may look like a callus and contains little black spots that are actually tiny blood vessels that have clotted.