
Hand, foot, and mouth disease is usually characterized by tiny blisters on the inside of the mouth and the palms of the hands, fingers, soles of the feet. It is commonly caused by coxsackievirus A16 (an enterovirus), and less often by other types of viruses.
Young children are primarily affected, but it may be seen in adults. Most cases occur in the summer and early fall. Outbreaks may occur among groups of children especially in child care centers or nursery schools. Symptoms usually appear 3 to 5 days after exposure.
People can spread the disease when they are shedding the virus in their feces. It is also spread by the respiratory tract from mouth or respiratory secretions (such as from saliva on hands or toys). The virus has also been found in the fluid from the skin blisters. The infection is spread most easily during the acute
phase/stage of illness when people are feeling ill, but the virus can be spread for several weeks after the onset of infection.
The rash appears as blisters or ulcers in the mouth, on the inner cheeks, gums, sides of the tongue, and as bumps or blisters on the hands, feet, and sometimes other parts of the skin. The skin rash may last for 7 to 10 days.

Source: Maryland Department of Health
For more information:
https://www.cdc.gov/hand-foot-mouth/index.html