Overview: Hand, Foot, and Mouth Disease (HMFD) is a common viral illness that usually affects infants and children younger than 5 years old. However, it can sometimes occur in adults. It is characterized by fever, sores in the mouth and a rash with blisters. Although the names are similar, Hand, Foot, and Mouth disease is NOT the same as Foot and Mouth Disease which affects cattle, sheep and swine. The two diseases are caused by different viruses.