Pachyonychia congenita (PC) is a rare inherited condition that primarily affects the nails and skin. The fingernails and toenails may be thickened and abnormally shaped. Affected people can also develop painful calluses and blisters on the soles of their feet and less frequently on the palms of their hands (palmoplantar keratoderma). Additional features include white patches on the tongue and inside of the mouth (leukokeratosis); bumps around the elbows, knees, and waistline (follicular hyperkeratosis); and cysts of various types including steatocystoma. Features may vary among affected people depending on their specific mutation. PC is divided into 5 types based on the specific keratin gene involved: PC-K6a, PC-K6b, PC-K6c, PC-K16, and PC-K17. All forms are inherited in an autosomal dominant manner. Treatment is based on the signs and symptoms present in each person.