Health Information



The flu is an infection of the nose, throat, and lungs. The influenza virus causes the infection.

See also: Swine flu (H1N1)

Alternative Names

Influenza A; Influenza B


Influenza A usually arrives between early winter and early spring. Influenza B can appear at any time of the year. H1N1, or swine flu, is another type of influenza.

Most people catch the flu when they breathe in tiny droplets from coughs or sneezes of someone who has the flu. It is also spread when you touch a something with the virus on it, then touch your mouth, nose, or eyes.

Symptoms appear 1 - 7 days later (usually within 2 - 3 days). The flu spreads easily. It often strikes a community all at once. Students or workers become sick within 2 or 3 weeks of the flu's arrival in a school or workplace.

Sometimes people confuse colds and flu. They do share some of the same symptoms. Most people get a cold several times each year. But they usually get the flu once every few years.

People call a viral illness that makes them throw up or have diarrhea "stomach flu." This is incorrect. The flu does not cause the stomach symptoms. The flu mostly causes symptoms in the nose, throat, and lungs.


The flu usually begins quickly. The first symptoms are a fever between 102 and 106 °F. (An adult usually has a lower fever than a child.)

Other common symptoms include:

  • Body aches
  • Chills
  • Dizziness
  • Flushed face
  • Headache
  • Lack of energy
  • Nausea and vomiting

Between day 2 and day 4 of the illness, the fever and "whole body" symptoms begin to fade.

Then breathing symptoms begin to increase. The symptom is usually not a dry cough. Most people also develop a sore throat and headache. Runny nose and sneezing are common. It is a clear, watery nasal discharge.

These symptoms (except the cough) usually go away in 4 - 7 days. Sometimes, the fever returns. The cough and feeling tired may last for weeks.

Some people may not feel like eating.

The flu can make asthma, breathing problems, and other long-term illnesses worse.

Exams and Tests

Most people of do not need to see a doctor or nurse when they have flu symptoms. This is because most people are not at risk for a severe case.

People who become very sick with the flu may want to see a health care provider. People who are at high risk for flu complications may also want to see a doctor if they get the flu.

When many people in an area have flu, a doctor can make a diagnosis after hearing the symptoms. No further testing is needed.

There is a test to detect the flu. It is done by swabbing the nose and throat. The results of this test can be available rapidly. Sometimes, this test can help your health care provider decide the best treatment.



Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) help lower fever. Sometimes doctors suggest you use both types of medicine. Do NOT use aspirin.

A fever does not need to come all the way down to normal. Most people will feel better when their temperature drops by even 1 degree.

Over-the-counter cold medicines may make some of your symptoms better. Cough drops will help with your sore throat.

You also need a lot of rest. Drink plenty of liquids. Avoid alcohol and tobacco.


Most people with milder symptoms feel better in 3 - 4 days. They do not need to see a doctor or take antiviral medications.

Doctors may give antiviral drugs to people who get very sick. People who are at high risk for problems from the flu may need these medicines.

These medicines may shorten the time you have symptoms by about 1 day. They work better if you start taking them within 2 days of your first symptoms.

Children at risk of a severe case of the flu may also need these medicines.

Outlook (Prognosis)

Millions of people in the United States get the flu each year. Most get better within a week or two.

But thousands become sick. They need to stay in the hospital. About 36,000 people die each year of problems from the flu.

Anyone at any age can have serious complications from the flu. Those at highest risk include:

  • People over age 50
  • Children between 6 months and 2 years
  • Women more than 3 months pregnant during the flu season
  • Anyone living in a long-term care facility
  • Anyone with chronic heart, lung, or kidney conditions, diabetes, or a weakened immune system

In most people who are healthy, the flu goes away within 7 - 10 days.

Possible Complications

Possible complications, especially for those at high risk, include:

When to Contact a Medical Professional

Call your health care provider if you get the flu and are at riks of having problems from it. Also call your doctor if your illness seems very bad.


You can take steps to avoid catching or spreading the flu.

Stay in your apartment, dorm room, or home for at least 24 hours after any fever is gone. Wear a mask if you leave your room.

Avoid sharing food, utensils, cups, or bottles. Cover your cough with a tissue and throw away after use. Carry hand sanitizer with you. Use it often during the day and always after touching your face.

Cough into your sleeve if a tissue is not available. Avoid touching your eyes, nose, and mouth.

Children older than 6 months, adolescents, and adults should get a flu shot every year.

The vaccine used in the 2010 - 2011 flu season will also protect against swine (H1N1) flu. The vaccine is available as a flu shot or a nasal spray-type flu vaccine.

For specific recommendations, see influenza vaccine.


Jefferson T, Jones M, Doshi P, Del Mar C. Neuraminidase inhibitors for preventing and treating influenza in healthy adults: systematic review and meta-analysis. BMJ. 2009 Dec 8;339:b5106.

Seasonal flu: what to do if you get sick. Centers for Disease Control and Prevention. Accessed October 4, 2010.

Review Date: 4/26/2011
Reviewed By: A.D.A.M. Editorial: David Zieve, MD, MHA, and David R. Eltz. Previously reviewed by David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine (10/5/2010).
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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