The flu (influenza) is a very contagious viral infection of the respiratory tract.

More to Know

In the United States, flu season runs from October to May. Most flu cases happen between late December and early March. Sometimes the flu is confused with the common cold, but flu symptoms start more suddenly and can be more severe.

Flu symptoms include fever, sore throat, headache, cough, weakness, muscle pain, and loss of appetite. Fever and other symptoms usually end after 5 days, but coughing and weakness may go on for up to another week. To cope with symptoms, drink lots of fluids, get plenty of rest, and take acetaminophen or ibuprofen to relieve fever and aches.

Sometimes, the flu is a serious illness, and can lead to pneumonia, dehydration, and other life-threatening problems. Infants, seniors, and people with long-term health problems are at the highest risk.

Keep in Mind

You can help protect your family from the flu by getting the flu vaccine every year. The Centers for Disease Control and Prevention (CDC) recommends it for most people over 6 months old.

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.