Hand, foot and mouth disease is a common childhood illness that can affect adults. It usually clears up by itself in 7 to 10 days. Dec 22, - Hand, Foot, and Mouth Disease (HFMD) Hand, foot, and mouth disease is a common viral illness that usually affects infants and children younger than 5 years old. However, it can sometimes occur in older children and adults. Typical symptoms of hand, foot, and mouth disease include fever, mouth sores, and a skin rash.