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The Manual's Editorial Staff

Reviewed/Revised May 2023
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What is asthma?

Asthma is a condition in which the breathing passages (airways) in your lungs get narrow. When the airways are narrow, it's hard to breathe. Breathing often makes a squeaky sound called wheezing Wheezing Wheezing is a high-pitched, whistling sound that occurs during breathing when the airways are partially blocked. (See also Wheezing in Infants and Young Children.) Wheezing results from a narrowing... read more .

  • Asthma happens in attacks that come and go

  • Exercise, household allergens, or breathing dust in the air can trigger asthma attacks

  • You wheeze and feel short of breath during an asthma attack

  • Asthma attacks vary from mild to severe to life threatening

  • During an asthma attack, you can take medicine that quickly opens your airway

  • To prevent asthma attacks, stay away from things that trigger your asthma

  • Some people take medicine to help prevent attacks

Inside the Lungs and Airways

Inside the Lungs and Airways

What causes asthma?

The Trachea and Bronchi

During an asthma attack, several things make your breathing passages narrow. The lining of your breathing passages swells up. Your airways fill with thick fluid (mucus). The muscles around your breathing passages tighten, which helps close off your airways.

Asthma usually runs in families and starts in childhood, but it can start at any time of life.

In people who have asthma, many things can trigger an attack. If you don't have asthma, these triggers won't cause you to get asthma.

Common asthma triggers include:

Other things are triggers only in some people:

What are the symptoms of an asthma attack?

Usually you feel fine until an attack starts. Attacks can be mild or severe.

Asthma symptoms may last for minutes, hours, or days. Most people recover with the right treatment, even from severe asthma attacks. However, asthma attacks can be fatal.

Common asthma symptoms:

  • A tight feeling in your chest

  • Wheezing

  • Shortness of breath

Sometimes coughing is the only symptom you’ll have.

Symptoms of a severe asthma attack include:

  • Struggling to breathe

  • Feeling like you can't get air in or out of your lungs

  • Confusion

  • Not enough air to walk or talk

  • Blue lips or fingers from low oxygen in the blood

If you have any of these symptoms of a severe asthma attack, call for emergency medical help (dial 911 in the United States) or go to a hospital emergency room right away.

A severe attack is life-threatening. You need fast, professional treatment. If you get severe asthma attacks, wear a medical alert bracelet or necklace. Always carry a cell phone to call 911 for emergency help.

How can doctors tell if I have asthma?

Doctors will usually suspect asthma based on your symptoms. To tell for sure if you have asthma, they’ll:

If you're having a severe attack, doctors will usually also check the level of oxygen in your blood. Sometimes they'll do a chest x-ray.

How do doctors treat asthma?

To treat mild asthma attacks yourself:

  • Use an inhaler with medicine to open your airways (called a bronchodilator): take 1 to 3 puffs—if 1 time doesn't help, wait about 20 minutes and use the inhaler again

  • Move into fresh air

  • Sit down and rest until you can breathe more easily

For severe asthma attacks, call 911 for emergency medical help or go to a hospital right away. Doctors will use medicine to quickly open your airways and may also:

  • Give you a bronchodilator medicine using a nebulizer, a special machine

  • Give you corticosteroids into your vein

  • Give you oxygen if your oxygen level is low

  • Have you stay in the hospital until you’re breathing better

Doctors usually use a medicine called albuterol for the bronchodilator, but sometimes they combine it with ipratropium as a second bronchodilator. If you're having too much trouble breathing to use a nebulizer, doctors may give you a shot of epinephrine, which is a fast-acting bronchodilator.

If the asthma attack is very severe, doctors may need to:

  • Put a tube through your mouth into your windpipe (called intubation) and put you on a ventilator

Doctors use many different medicines to treat asthma. They may give you the medicine using:

  • Metered-dose inhalers

  • Nebulizers

It is very important to use the inhaler or nebulizer the right way or the medicine won't reach your airways. Your doctor or health care worker can teach you the right way to use these devices.

Metered-dose inhalers

Metered-dose inhalers are the most common way to get asthma medicines. They turn a dose of medicine into a fine spray that you can breathe in.

It's best to use a spacer or holding chamber to get the right amount of medicine to your lungs. Inhalers are small enough to carry in a purse or backpack.

Metered Dose Inhaler

  • Shake the inhaler after removing the cap.

  • Breathe out for 1 or 2 seconds.

  • Put the inhaler in your mouth or 1 to 2 inches from it and start to breathe in slowly, like sipping hot soup.

  • While starting to breathe in, press the top of the inhaler.

  • Breathe in slowly until your lungs are full. (This should take about 5 or 6 seconds.)

  • Hold your breath for 10 seconds (or as long as you can).

  • Breathe out and, if a second dose is required, repeat the procedure after 1 minute.

  • If you find it difficult to coordinate breathing using this method, a spacer can be used.

Metered Dose Inhaler


Nebulizers are electric or battery-powered machines that turn liquid medicine into a fine spray that you breathe in.

How do you prevent asthma?

To help prevent asthma attacks:

  • Avoid triggers as much as you can, particularly cigarette smoke

  • Use the preventive medicines your doctor prescribes

  • If exercise triggers your asthma, use your bronchodilator inhaler just before you exercise

Sometimes you can get triggers out of your house by removing rugs, pillows, curtains, and other fabric items that may hold dust. Keep your house very clean and use a dehumidifier. If you're allergic to your pet, you may need to find a new home for it.

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