Callus provides a natural protection of the soft vulnerable subepidermal tissues. Relatively smooth areas of callus are found regularly on normal feet and cause no problems when the skin is hydrated. Thin smooth areas of callus are protective. However, when the callus forms irregular lumps, it acts like a pebble in the shoe and causes underlying ulceration, especially in the sensory impaired foot in which pain perception may be inadequate to attract attention. Blood or fluid escaping from under a callus indicates that an ulcer is present.