What Is the Flu?

Flu is the common name for influenza. It's caused by a virus that infects the nose, throat, and lungs.

Often, when you're sick with a virus, your body builds a defense system by making antibodies against it. That means you usually don't get that particular type of virus again. Unfortunately, flu viruses mutate (change) each year. So getting sick once doesn't protect you from the flu forever.

Some years, the change in the flu virus is slight. So if you do get the flu, it's mild. The antibodies from having the flu before give you some protection. But other years, the flu virus goes through a major change and many people get very sick.

When Is Flu Season?

Flu viruses usually cause the most illness during the colder months of the year. In the United States, flu season is from October to May. Kids get the flu most often. But people in every age group — including teens — can catch it.

How Does the Flu Spread?

The flu virus spreads through the air when a person who has the virus sneezes, coughs, or speaks. The flu can sometimes spread through objects that someone with the virus touched, sneezed, or coughed on. When a healthy person touches these contaminated items and then touches their mouth or nose, the virus can enter their body.

People carrying the virus can be contagious from the day before their symptoms start until about a week later. So it's possible to spread the flu before you know you're sick.

Viruses like the flu virus can spread easily in schools. Then, students can bring the virus home to family members and people around them, spreading the illness in their communities.

What Are the Signs & Symptoms of the Flu?

Flu symptoms start about 2 days after a person was exposed to the virus. The main symptoms are:

  • headache
  • sore throat
  • a high fever that comes on suddenly
  • chills
  • muscle aches
  • stuffy nose
  • dry cough
  • feeling very tired or weak
  • loss of appetite

The fever and aches usually stop in a few days. But the sore throat, cough, stuffy nose, and tiredness may go on for a week or more.

The flu also can cause vomiting, belly pain, and diarrhea. But if you have only vomiting and diarrhea without the other flu symptoms, you probably have gastroenteritis. Gastroenteritis, often called the "stomach flu," isn't the same as influenza. It's usually caused by common viruses that we come into contact with every day.

How Is the Flu Diagnosed?

Based on your symptoms and how you look, your doctor usually can tell if you have the flu. Most people who have it look ill and miserable.

Other infections can cause symptoms similar to the flu. So if a doctor needs to be sure that someone has the flu, they might do a test. They'll take a sample of mucus by wiping a long cotton swab inside the nose or throat. Results might be ready quickly, or can take longer if the test is sent to a lab.

You may feel miserable if you get the flu, but it's unlikely to be serious. It's rare that healthy teens get other problems from the flu. Older adults (over age 65), young kids (under age 5), and people with ongoing medical conditions are more likely to become seriously ill with the flu.

What Should I Do if I Have the Flu?

If you get the flu, the best way to take care of yourself is to rest in bed and drink lots of liquids like water and other non-caffeinated drinks. Stay home from school until you feel better and your temperature has returned to normal.

Most people get better on their own after the virus runs its course. But call your doctor if you have the flu and:

  • You're getting worse instead of better.
  • You have trouble breathing.
  • You have a medical condition (such as diabetes, heart problems, asthma, or other lung problems).

Most teens can take acetaminophen or ibuprofen to help with fever and aches. Don't take aspirin or any products that contain aspirin, though. If kids and teens take aspirin while they have the flu, it puts them at risk for Reye syndrome , which is rare but can be serious.

Antibiotics don't work on viruses, so they won't help someone with the flu get better. Sometimes doctors can prescribe an antiviral medicine to cut down how long a person is ill from the flu. These medicines are effective only against some types of flu virus and work best when taken within 48 hours of when symptoms start. Doctors usually use this medicine for people who are very young, elderly, or at risk for serious problems, like people with asthma.

Can the Flu Be Prevented?

There's no guaranteed way to avoid the flu. But getting the flu vaccine can help. Everyone 6 months of age and older should get it every year.

Flu vaccines are available as a shot or as a nasal spray. Both work equally well. This flu season (2020–2021), get whichever vaccine your doctor recommends. People with weak immune systems or some health conditions (such as asthma) and pregnant women should not get the nasal spray vaccine.

What else can you do? Wash your hands well and often. Avoid sharing cups, utensils, or towels with others. If you do catch the flu, use tissues whenever you sneeze or cough to avoid spreading the virus.

During the coronavirus pandemic, experts found that wearing masks can help protect the community from the spread of germs. They recommend that everyone wear a mask when out in public or around people who don't live with them. Wearing masks can also help stop the spread of flu.

If you do get the flu this season, take care of yourself and call your doctor with any questions or concerns. When you're feeling bad, remember that the flu usually lasts a week or less and you'll be back to normal before too long.

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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.