Hand, foot, and mouth disease (HFMD) is most contagious during the first week of illness, especially when the infected person has a fever and symptoms like mouth sores and rash. After the first week, the contagiousness decreases but the virus can still be spread through contact with blisters, saliva, and stool for several weeks. Typically, a person is considered not contagious and safe to return to normal activities once they have been fever-free for at least 24 hours, and all blisters have healed. However, good hygiene practices like frequent handwashing are important because the virus can remain in stool for weeks and still pose a risk of transmission.

In summary:

• Most contagious: First week of illness, especially with fever.
• Contagiousness lessens after fever and symptoms improve.
• Virus can still be present in stool for weeks.
• Safe to consider not contagious after fever-free for 24 hours and blisters are healed.
• Maintain good hygiene to prevent spread.

This means the contagious period is roughly 7 to 10 days, but caution is advised until blisters heal and hygiene is maintained.