Hand-foot-and-mouth disease: A common viral illness usually seen in infants and children characterized by a rash on the hands and feet and in the mouth. The internal rash (enanthem) consists of blisters and little ulcers. These may involve not only the lining of the mouth but also the gums, palate, and tongue. The external rash on the body (exanthem) typically affects the hands, the feet, and sometimes the buttocks. There may also be sore throat, irritability, decreased appetite, and fever. Hand-foot-and-mouth disease is caused by various viruses, including several types of coxsackievirus: most often Coxsackievirus A16, but also other coxsackieviruses and enterovirus 71. The incubation period is short, usually 4 to 6 days. The disease occurs most frequently in summer and fall. The illness is characteristically mild and self-limited. Also known as hand-foot-and-mouth syndrome and hand, foot, and mouth disease or syndrome.