Asthma Causes: What You Need to Know

Most people with asthma understand asthma triggers. But do you know what causes asthma in the first place?

a Latino woman standing outside on a sunny day uses an asthma inhaler

Medically reviewed in March 2022

Updated on April 22, 2022

Asthma symptoms can crop up when your airways become inflamed and narrowed, causing wheezing, coughing, and chest tightness. When you have asthma, your airways may be more sensitive to triggers, which are certain substances or environmental factors that don’t usually bother people without asthma.

But the underlying causes of asthma—and why it occurs in some people and not others—have long baffled medical experts. Read on for the latest understanding on asthma risk factors and triggers.

How do you get asthma?
According to the American Lung Association, the most common risk factors for asthma include allergies, having a close family member with asthma (especially a parent), having severe respiratory infections when you were a child, exposure to smoking and certain lung irritants, and being overweight or obese.

Allergies and asthma
Allergic asthma is when your body’s immune system mistakenly reacts to allergens (otherwise harmless substances in your environment), triggering allergic reactions and asthma symptoms.

It’s the most common form of asthma: Almost 90 percent of children with asthma and 50 percent of adults with asthma have allergic asthma.

"Once you have one allergy—skin, food, nose, eyes—you're at greater risk for developing other allergies and, in this case, asthma," says Neil L. Kao, MD, of the Allergic Disease and Asthma Center in Greenville, South Carolina, and a fellow with the American Academy of Allergy, Asthma and Immunology.

It makes sense that having nasal allergies like hay fever can increase your likelihood of developing asthma: The nose and lower airways are part of the same respiratory system, and they can react the same way as the lungs do to allergens, irritants, and viruses.

Eye, skin, and food allergies also go hand in hand with asthma. Like the mucus membranes in your nose and airways, the membranes in your eyes can be sensitive to allergens. Studies also show that there is a correlation between skin allergies and asthma. In fact, children who have eczema and hay fever are nine times more likely to have asthma as adults. And while it’s not entirely clear whether food allergies actually cause asthma, they can increase your risk for more severe asthma. In the United States, the most common food allergies are to milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, and soybeans.

Family history
Your chances of developing asthma increase significantly when asthma runs in your family. In fact, having a parent with asthma may increase your chances of developing asthma by three to six times compared to someone whose parents do not have asthma. That may not be so surprising, given that over 100 genes may be associated with allergic asthma, the most common type of asthma.

Not everyone with these genes develops asthma. In some people, environmental factors like smoking and respiratory infections may tip things off.

Viral respiratory infections
Certain types of viral respiratory infections during infancy and childhood may cause wheezing and lead to asthma later on, especially when infections are more severe and affect the lower parts of the respiratory tract.

Some children also have hyperactive airways, which can be triggered by infections. This means their bronchial airways overrespond to various stimuli by becoming inflamed and narrow. It's a similar condition to asthma and having hyperactive airways may increase your chances of developing asthma as an adult.

Smoking and lung irritants
Smoking can increase your risk of developing asthma. Smoking irritates and damages your airways and destroys your lung’s natural defenses against dirt and germs. Whether it’s first- or second-hand, smoking can stimulate the production of mucus in the lungs, a part of the asthma response that makes it difficult to breathe. Children who grow up around smokers and whose mothers smoked during pregnancy are more likely to develop asthma than kids whose parents don't smoke.

Many kinds of smoke and lung irritants can cause problems: tobacco smoke, vaping, smog, and exposure to dusts, chemical fumes, or vapors at work.

"It doesn't matter whether it's smoke from a cigarette or a pipe or even a burning building," Dr. Kao says. "Smoke is made up of chemicals and particulate matter that can irritate your lungs."

Overweight and obesity
You may know that obesity can increase your risk for arthritis, diabetes, stroke, and other health conditions, but did you know you can add asthma to that list as well? It's true, although it's not entirely clear why.

It could be that excess weight presses on the lungs, triggering responses typical of asthma. It might also be that extra weight can cause low-grade inflammation throughout your body, including your lungs. Obesity can also make asthma more severe, and harder to control.

While weight gain is a natural and healthy part of pregnancy, being obese or gaining more than your healthcare provider (HCP) recommends can mean harder work for your lungs. That might include the baby pressing on the diaphragm, the extra pounds the lungs must support, and the growing fetus for which the lungs must now also breathe, according to Kao. Hormonal changes during pregnancy also play a role and can affect immune system functioning. Obesity during pregnancy can also increase the baby’s risk for childhood asthma. 

Multiplication matters
Other factors may increase your risk for asthma. For example, the likelihood of developing asthma can depend on your age and sex. Before puberty, asthma is more common in males. After adolescence, there’s a switch and asthma becomes more prevalent in women than in men. But the distribution of asthma by sex levels out with time.

"Asthma occurs at all ages of life,” Kao says. "After about 50ish, occurrence is about even in men and women." Still, women tend to have more severe symptoms than men, and they're at greater risk for deadly asthma (possibly because of monthly hormonal fluctuations). 

The more risk factors you have, the more likely you are to develop asthma. If you have any of these risk factors and experience symptoms like coughing, wheezing, chest tightness, shortness of breath, or excess mucus or phlegm, talk to your HCP. Even if you don't have asthma symptoms, your HCP may be able to suggest strategies for lowering your risk of an asthma attack.

Article sources open article sources

National Institutes of Health. Asthma. Accessed April 15, 2022.
American Lung Association. Asthma risk factors. Page last reviewed October 23, 2020.
National Institutes of Health. Allergic asthma. Accessed April 15, 2022.
Martin PE, Matheson MC, Gurrin L, et al. Childhood eczema and rhinitis predict atopic but not nonatopic adult asthma: a prospective cohort study over 4 decades. J Allergy Clin Immunol. 2011;127(6):1473-9.e1.
Foong RX, du Toit G, Fox AT. Asthma, Food Allergy, and How They Relate to Each Other. Front Pediatr. 2017;5:89. Published 2017 May 9.
US Food and Drug Administration. Food allergies. Page last reviewed April 18, 2022.
McLeish AC, Cougle JR, Zvolensky MJ. Asthma and cigarette smoking in a representative sample of adults. J Health Psychol. 2011;16(4):643-652.
Wang H, Li N, Huang H. Asthma in Pregnancy: Pathophysiology, Diagnosis, Whole-Course Management, and Medication Safety. Can Respir J. 2020;2020:9046842. Published 2020 Feb 22.
Forno E, Celedón JC. The effect of obesity, weight gain, and weight loss on asthma inception and control. Curr Opin Allergy Clin Immunol. 2017;17(2):123-130.

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