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The Asthma and Allergy Foundation of America

800.7.ASTHMA (727.8462)


National Heart, Lung, and Blood Institute



Asthma is a chronic disease that causes the airways to narrow. Airflow is limited due to inflammation in the airways.



Asthma Attack




Peak Flow



Image of girl at a doctor visit.

•  Your medical history

•  Your family’s medical history

•  Your symptoms

•  A physical exam

•  Lung function tests in persons age 5 years and older

•  Other tests to check for conditions that have symptoms of asthma, but are not asthma


•  A cough lasts more than a week. Coughing may be the only symptom. It often occurs at night or early in the morning.

•  Shortness of breath. Breathing gets harder and may hurt. It is harder to breathe out than in.

•  Wheezing (high pitched whistling sound)

•  Tightness in the chest

Causes & Risk Factors

•  Genetic Factors. You are more likely to have asthma if other members of your family have or had it.

•  Environmental Factors. Being exposed to certain things can set off an immune system response for asthma to develop. Examples are house-dust mites and viral respiratory infections.


A doctor diagnoses asthma from:

Reasons to Call Doctor

Call your doctor when you feel the first change in your asthma status. Deal with a problem early to help prevent a severe problem.

•  You have asthma and have a cold or a fever.

•  You cough up mucus that is bloody-colored, green, or yellow.

•  An asthma attack does not respond to your medication.

•  Medication is not helping like it used to.

•  Your peak expiratory flow (PEF) numbers are in the yellow zone.

•  You have a harder time breathing or you are short of breath more often than before.

•  You breathe faster than usual.

•  Your asthma attacks are coming more often or are getting worse.

•  You use your rescue medication more than 2 times a week.

Reasons to Get Medical Care Fast

•  Your peak expiratory flow (PEF) numbers are in the red zone.

•  You have a fever with heavy breathing.

•  You have extreme shortness of breath. It may feel as if you can’t breathe at all. Or, you can’t say 4 or 5 words because you are so short of breath. Call 911!

•  You cough so much that you can’t take a breath. Call 911!

•  Your lips or fingernails are bluish in color. Call 911!

Focus on breathing slow and easy until you get medical care. Sit upright. Try to remain as calm and relaxed as you can.

Peak Flow Meters

These devices measure peak expiratory flow (PEF). PEF is the amount of air blown out after taking a deep breath. Your PEF readings can tell you and your health care provider:

•  About asthma triggers

•  If an asthma attack is starting. PEF is decreased with an asthma attack.

•  If your medicine plan is working

•  When to add or stop medicine

•  How severe your asthma is

Use your peak flow meter, as directed by your doctor or health care provider.

Find Your Personal Best Peak Flow Number

Your personal best peak flow number is the highest peak flow number you can get over a 2-week period when your asthma is under good control. Good control is when you feel good and do not have any asthma symptoms.


Take peak flow readings:

•  Twice a day for 2 weeks – when you wake up and  about 10 to 12 hours later

•  Before and after taking an inhaled beta2-agonist (if you take this medicine)

•  As advised by your doctor or health care provider

The Peak Flow Zone System

Once you know your personal best peak flow number, your health care provider will give you the numbers that tell you what to do. The peak flow numbers are put into zones that are set up like a traffic light.

Green Zone (80 to 100 percent of your personal best number). This signals all clear. No asthma symptoms are present, and you may take your medicines as usual.

Yellow Zone (50 to 80 percent of your personal best number). This signals caution. You may need to take more of your asthma medicine(s) to treat your asthma. Or, your overall asthma may not be under control, and the doctor may need to change your asthma action plan.

Red Zone (below 50 percent of your personal best number). This signals a medical alert. You must take an inhaled beta2-agonist right away and call your doctor without delay if your peak flow number does not return to the Yellow or Green Zone and stay in that zone.

This website is not meant to substitute for expert medical advice or treatment. Follow your doctor’s or health care provider’s advice if it differs from what is given in this guide.


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