What Causes Asthma? Common Triggers Explained

No one really knows what causes asthma. What we do know is that asthma is a chronic inflammatory disease of the airways. The causes can vary from person to person. Still, one thing is consistent: When airways come into contact with a trigger, they become inflamed, narrow, and fill with mucus.

How Asthma Attacks Happen

When you have an asthma attack, your airways narrow and it gets hard to breathe. This can result from spasms of the muscles around the airways, inflammation and swelling of the mucosal membrane that lines them, or high amounts of mucus inside them. You might have shortness of breath, wheeze or cough as your body tries to get rid of mucus.

Why do you have asthma and your friend doesn't? No one knows for sure. Allergies play a role for many people as do genetics.

If you or a loved one has asthma, it's important to understand what your triggers are. Once you figure that out, you can take steps to avoid them. As a result you’ll have fewer and less severe asthma attacks.

Asthma Triggers

Some known triggers of asthma attacks include:

  • Allergies
  • Food and Food Additives
  • Exercise
  • Heartburn
  • Smoking
  • Sinusitis
  • Medications
  • Weather
  • Smoke

Allergies Can Cause Asthma

Allergies with asthma is a common problem. Eighty percent of people with asthma have allergies to things in the air, like tree, grass, and weed pollens, mold, animal dander, dust mites, and cockroach droppings. In one study, children with high levels of cockroach poop in their homes were four times more likely to have childhood asthma than children with low levels. An allergy to dust mites is another common asthma trigger.

Food and Food Additives Trigger Asthma

Food allergies can cause mild to severe life-threatening reactions. They rarely cause asthma without other symptoms. If you have food allergies asthma can be part of a severe, life-threatening reaction called anaphylaxis. The most common foods associated with allergic symptoms are:

  • Eggs
  • Cow's milk
  • Peanuts
  • Tree nuts
  • Soy
  • Wheat
  • Fish
  • Shrimp and other shellfish
  • Salads
  • Fresh fruits

Food preservatives can trigger isolated asthma, especially sulfite additives, like sodium bisulfite, potassium bisulfite, sodium metabisulfite, potassium metabisulfite, and sodium sulfite, which are commonly used in food processing or preparation.


Exercise-Induced Asthma

For about 80% of people with asthma, a heavy workout can cause airways to narrow. Exercise is often the main asthma trigger. If you have exercise-induced asthma, you will feel chest tightness, cough, and have trouble breathing within the first 5 to 15 minutes of an aerobic workout. For most people these symptoms go away in the next 30 to 60 minutes of exercise. But up to 50% of people with exercise-induced asthma may have another attack 6 to 10 hours later. A slow warm up may help prevent this.

Heartburn and Asthma

Severe heartburn and asthma often go hand-in-hand. Up to 89% of people with asthma also have severe heartburn (you might hear your doctor call it gastroesophageal reflux disease, or GERD). It usually happens at night when you're lying down. Normally a valve prevents stomach acids from backing up into your esophagus (the tube food goes down when you eat). When you have GERD, this valve doesn't work like it should. Your stomach acids reflux, or back up, into the esophagus. If the acids reach your throat or airways the irritation and inflammation they cause could trigger an asthma attack.

Certain clues that suggest reflux as the cause of asthma include the onset of asthma in adulthood, no family history of asthma, no history of allergies or bronchitis, difficult-to-control asthma, or coughing while lying down.

If your doctor suspects this problem, they may recommend specific tests to look for it, change your foods, or offer you medications.

Smoking and Asthma

People who smoke cigarettes are more likely to get asthma. If you smoke with asthma, it may make symptoms like coughing and wheezing worse. Women who smoke during pregnancy increase the risk of wheezing in their babies. Babies whose mothers smoked during pregnancy also have worse lung function. If you have asthma and you're a smoker, quitting is the most important step you can take to protect your lungs.

Sinusitis and Other Upper Respiratory Infections

Much like asthma causes inflammation in the lining of your airways, sinusitis causes inflammation in the mucus membranes that line your sinuses. This makes the membranes put out more mucus. If you have asthma and your sinuses get inflamed, your airways may too. Prompt treatment of a sinus infection can relieve asthma symptoms.


Infections and Asthma

Cold, flu, bronchitis, and sinus can cause an asthma attack. These respiratory infections that trigger asthma can be viral or bacterial. They're a common cause of asthma, especially in children under age 10. You may be more likely to have an attack for up to two months after an upper respiratory infection. Anywhere from 20% to 70% of adults with asthma also have sinus disease. Also, 15% to 56% of people with allergic rhinitis (hay fever) or sinusitis also have signs of asthma.

Medications and Asthma

People with aspirin-sensitive asthma may also be have trouble with other medications like anti-inflammatory drugs (ibuprofen, naproxen) and beta-blockers (used to treat heart disease, high blood pressure, and glaucoma). If you know you're sensitive to these drugs, make sure your doctor notes the problem on your chart. Always talk to your pharmacist about this reaction before you start a new medication.

Other Asthma Triggers

Irritants. Tobacco smoke, smoke from wood-burning appliances or fireplaces, strong odors from perfumes, cleaning agents, etc., can all trigger asthma. So can air pollution, workplace dust, or fumes from chemicals

Weather. Cold air, changes in temperature, and humidity can cause an attack.

Strong emotions. Stress and asthma are often seen together. Anxiety, crying, yelling, stress, anger, or laughing hard can bring on an asthma attack.

How Do Triggers Make Asthma Worse?

When you have asthma, your airways are always inflamed and sensitive. They react to a variety of external factors, or triggers. Contact with these triggers is what causes asthma symptoms. You airways tighten and get more inflamed, mucus blocks them, and your symptoms get worse. An asthma attack can start right after exposure to a trigger or several days or even weeks later.

Reactions to asthma triggers are different for each person and vary from time to time. Something may bother you, but not your friend with asthma. You might have many triggers while they have none. And while avoiding triggers is a good way to control asthma, the best way is take medications and follow treatments exactly as prescribed by your doctor in your asthma action plan.


How Can I Tell What Causes and Triggers My Asthma?

Figuring out what was going on around you when you had an attack is the first step to identifying your triggers. 

Your doctor may also do blood testing or ask you to use a device called a peak flow meter. It measures how much air you exhale and how quickly it comes out. It can alert you to changes in your breathing and the onset of asthma symptoms.

Ask your asthma doctor if using a peak flow meter would help you narrow down the causes of your asthma.

WebMD Medical Reference Reviewed by Smitha Bhandari, MD on September 13, 2020


National Heart Lung and Blood Institute: "Causes of Asthma." 
American Academy of Allergy Asthma & Immunology: "Causes of Asthma." 
Murray, J. and Nadel, J. Textbook of Respiratory Medicine, Third edition, W.B. Saunders Company, 2000. 

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