What is the flu?

What is the flu? — The flu is an infection that can cause fever, cough, body aches, and other symptoms. The most common type of flu is the "seasonal" flu. There are different forms of seasonal flu, for example, "type A" and "type B."

All forms of the flu are caused by viruses. The medical term for the flu is "influenza."

What are the other types of flu?

Besides seasonal flu, there is also the "swine" flu, which caused a worldwide outbreak ("pandemic") in 2009 and 2010, and the bird flu. Bird flu (also known as "avian flu") is a severe form of the flu that is caused by a type of flu virus that first infected birds.

What are the most common flu symptoms?

All forms of the flu can cause

  • Fever (temperature higher than 100ºF or 37.8ºC)
  • Extreme tiredness
  • Headache or body aches
  • Cough
  • Sore throat
  • Runny nose

Flu symptoms can come on very suddenly.

Is the flu dangerous?

It can be. Most people get over the flu on their own, without any lasting problems. But some people need to go to the hospital because of the flu. And some people even die from it. This is because the flu can cause a serious lung infection called pneumonia. That's why it's important to keep from getting the flu in the first place.

People at higher risk of getting very sick from the flu include:

  • People 65 or older
  • Young children (under 5 years old, and especially under 2 years old)
  • Pregnant women
  • People with certain other medical problems

If you or your child is in one of these groups, talk to a doctor or nurse. He or she can help you decide if you or your child needs treatment. In some cases, family members of a person with the flu might also need medicine to help prevent them from getting it.

Is there a test for flu?

Yes. There are tests for the flu. In most cases, your doctor can tell if you have the flu by your symptoms. But in some cases – for example, if you are at risk for having other problems caused by the flu – your doctor might do a test for flu.

How can I protect myself from the flu?

You can:

  • Wash your hands often with soap and water. The table has instructions on how to wash your hands to prevent spreading illness (table 1).
  • Stay away from people you know are sick
  • Get the flu vaccine every year – Some years the flu vaccine is more effective than others. But even in years when it is less effective, it still helps prevent some cases of the flu. It can also help keep you from getting severely ill if you do get the flu.

Table 1: Hand washing to prevent spreading illness

Wet your hands and put soap on them
Rub your hands together for at least 20 seconds. Make sure to clean your wrists, fingernails, and in between your fingers.
Rinse your hands
Dry your hands with a paper towel that you can throw away

If you are not near a sink, you can use a hand gel to clean your hands. The gels with at least 60 percent alcohol work the best. But it is better to wash with soap and water if you can.

What should I do if I get the flu?

If you think you have the flu, stay home, rest, and drink plenty of fluids. You can also take acetaminophen (sample brand name: Tylenol) to relieve fever and aches.

Do not give aspirin or medicines that contain aspirin to children younger than 18. In children, aspirin can cause a serious problem called Reye syndrome.

Most people with the flu get better on their own within 1 to 2 weeks. But you should call your doctor or nurse if you:

  • Have trouble breathing or are short of breath
  • Feel pain or pressure in your chest or belly
  • Get suddenly dizzy
  • Feel confused
  • Have severe vomiting

Take your child to the doctor if he or she:

  • Starts breathing fast or has trouble breathing
  • Starts to turn blue or purple
  • Is not drinking enough fluids
  • Will not wake up or will not interact with you
  • Is so unhappy that he or she does not want to be held
  • Gets better from the flu but then gets sick again with a fever or cough
  • Has a fever with a rash

If you decide to go to a walk-in clinic or a hospital because of the flu, tell someone right away why you are there. The staff might ask you to wear a mask or to wait someplace where you are less likely to spread your infection.

Whether or not you see a doctor or nurse, you should stay home while you are sick with the flu, or keep your child home if he or she is sick. Do not go to work or school until your fever has been gone for at least 24 hours, without taking medicine such as acetaminophen. If you work with patients, such as in a hospital or clinic, you might need to stay home longer if you are still coughing. Also, always cover your mouth and nose with the inside of your elbow when you cough or sneeze.


Yes, people with the flu can get medicines called antiviral medicines. These medicines can help people avoid some of the problems caused by the flu. Not every person with the flu needs an antiviral medicine, but some people do. Your doctor or nurse will decide if you need an antiviral medicine. Antibiotics do not work on the flu.

What if I am pregnant?

The flu can be very dangerous for pregnant women. If you are pregnant, it is very important that you get the flu vaccine. You should also avoid taking care of anyone who has the flu.

If you are pregnant, call your doctor or nurse right away if:

  • You might have been near someone with the flu.
  • You think you might be coming down with the flu. In pregnant women, the symptoms of the flu can get worse very quickly. The flu can even cause trouble breathing or lead to death of the woman or her baby. That is why it is so important that you talk to doctor or nurse as soon as you notice any of the flu symptoms listed above. You will need an antiviral medicine if you are pregnant and have the flu.

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This information is not specific medical advice and does not replace information you receive from your health care provider. This is only a brief summary of general information. It does NOT include all information about conditions, illnesses, injuries, tests, procedures, treatments, therapies, discharge instructions or life-style choices that may apply to you. You must talk with your health care provider for complete information about your health and treatment options. This information should not be used to decide whether or not to accept your health care provider's advice, instructions or recommendations. Only your health care provider has the knowledge and training to provide advice that is right for you.The use of UpToDate content is governed by the UpToDate Terms of Use. ©2021 UpToDate, Inc. All rights reserved.


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