Flu

Source: MedlinePlus Health Topics, U.S. National Library of Medicine

Last synced 8/14/2026Status: primary verified

What is the flu? The flu, also called influenza, is a respiratory infection caused by viruses. Each year, millions of Americans get sick with the flu. Sometimes it causes mild illness. But it can also be serious or even deadly, especially for people over 65, newborn babies, and people with certain chronic illnesses. What causes the flu? The flu is caused by flu viruses that spread from person to person. When someone with the flu coughs, sneezes, or talks, they spray tiny droplets. These droplets can land in the mouths or noses of people who are nearby. Less often, a person may get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes. What are the symptoms of the flu? Symptoms of the flu come on suddenly and may include: Fever or feeling feverish/chills Cough Sore throat Runny or stuffy nose Muscle or body aches Headaches Fatigue (tiredness) Some people may also have vomiting and diarrhea . This is more common in children. Sometimes people have trouble figuring out whether they have a cold or the flu. There are differences between them: Signs and Symptoms Cold Flu Start of symptoms Slowly Suddenly Fever Rarely Usually Aches Sometimes (slight) Usually Fatigue, weakness Sometimes Usually Headache Rarely Common Stuffy nose, sneezing, or sore throat Common Sometimes Sometimes people say that they have a "flu" when they really have something else. For example, "stomach flu" isn't the flu; it's gastroenteritis . What other problems can the flu cause? Some people who get the flu will develop complications. Some of these complications can be serious or even life-threatening. They include: Bronchitis Ear infection Sinus infection Pneumonia Inflammation of the heart (myocarditis), brain ( encephalitis ), or muscle tissues ( myositis , rhabdomyolysis) The flu also can make chronic health problems worse. For example, people with asthma may have asthma attacks while they have flu. Certain people are more like

Educational only

This information is for general education and is not medical advice. Always talk to a licensed U.S. clinician about your situation, medications, or treatment decisions.