Causes and Risk Factors of Asthma

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Though asthma is common, what causes it isn't fully understood. It's likely there is a genetic component that predisposes a person to develop the disease, but typically certain environmental factors must also be in place.

But although experts may not know for sure why one person has asthma and another doesn't, they do understand the changes in the body that lead to asthma symptoms—bronchoconstriction (narrowing of the bronchi, or airways) and excess mucus production that together restrict airflow.

There also are a variety of known risk factors for asthma, such as excess weight, as well as many common triggers ranging from allergens like dust mites and mold to exercise and respiratory infections such as a common cold.

This article describes what's currently known about the risk factors for asthma.

Inhaling through nebulizer at doctor's office!
skynesher / Getty Images

Risk Factors for Asthma

You are at an increased risk of having asthma if you:

  • Have a family history of asthma
  • Had certain types of viral respiratory infections as a baby or young child
  • Have eczema (atopic dermatitis) or allergies, such as hay fever (allergic rhinitis)
  • Are exposed to dust or chemical fumes in your work
  • Currently smoke or did in the past, your mother smoked while pregnant with you, or you've been exposed to secondhand smoke
  • Have been exposed to air pollution (specifically ozone)
  • Are overweight, which can lead to worse symptoms and less effective control of the condition
  • Were born prematurely or had a low birth weight

Among children, asthma is more common in males than females. By adulthood, this is reversed, and females are more likely to have asthma.

Asthma Disparities

Racial and ethnic minority groups experience a disproportionate burden of asthma. Black and Latinx people and American Indian/Alaska Natives are more likely to develop asthma compared to White Americans. Puerto Ricans have particularly high rates of asthma, nearly twice that of non-Hispanic Whites.

Black Americans are five times more likely to be hospitalized for asthma compared to White Americans, and three times as likely to die from it. Black women have the highest risk of death from asthma of all groups.

The reasons for these disparities are varied and include less access to health care, poorer quality care, increased exposure to indoor and outdoor triggers, and higher levels of stress.

Atopic March

Infants who have atopic dermatitis sometimes go on to develop hay fever and asthma—especially if they experienced wheezing as babies. This phenomenon is referred to as atopic march or progressive atopy.

It's thought that the barrier that skin usually provides against allergy-triggering substances (allergens) is less effective in children with eczema, allowing them to become sensitized.


It is well-established that asthma runs in families, which suggests that the condition has a significant genetic component. More than 100 genes have been associated with allergic asthma, most of which are involved in immune reactions and lung functions.

However, the presence of any of these genes in a person's DNA does not guarantee they will have asthma; it only means they're at an increased risk. It typically requires exposure to an environmental trigger for asthma to develop.

You are three to six times more likely to have asthma if one of your parents has asthma, according to the American Lung Association.

Asthma Triggers

The potential causes of asthma symptoms and asthma attacks in those who have the condition are as variable and unique to each individual as are the factors that put them at risk in the first place. There's a wide variety of such triggers, and many people have more than one.

Indoor Triggers

Your home may harbor any of several common allergens known to bring on asthma symptoms.

  • Dust mites: Dust mites (Dermatophagoides pteronyssinus) are microscopic insects that exist in every home and feed on tiny flakes of skin and hair found on bedding (mattresses, pillows, bed covers), carpets, upholstered furniture or anything covered in fabric, and stuffed toys.
  • Mold: Mold is most often found on wet or damp surfaces in bathrooms, kitchens, and basements.
  • Cockroaches and other pests: Body parts, urine, and droppings of cockroaches and pests contain proteins that can trigger allergy symptoms.
  • Pets: Allergens from your pets' dead skin, droppings, urine, and saliva can trigger asthma.
  • Secondhand smoke: Environmental tobacco smoke contains more than 250 different chemicals, including benzene, vinyl chloride, and arsenic, that may irritate airways and bring on asthma symptoms.
  • Nitrogen dioxide: Nitrogen dioxide is a gas released by gas stoves, fireplaces, and gas space heaters. It can irritate lungs and lead to shortness of breath.

Outdoor Triggers

During the spring and fall, airborne pollens and molds commonly trigger asthma symptoms, among them:

  • Pollen: Pollens are small, powdery granules that are essential for plant fertilization. Pollens from many different kinds of grasses, weeds, and trees may trigger allergy and asthma symptoms. The season and weather conditions greatly influence the amount of pollen in the air. Pollen season varies depending on location but typically lasts from February to October.
  • Mold: Mold growing in soil or on outdoor vegetation can become airborne and trigger asthma symptoms.
  • Weather: Certain weather conditions can make asthma triggers more problematic. Pollen is particularly plentiful when it's hot, dry, and windy outside, for example. Mold thrives in rainy or humid weather. Dry, cold, or windy weather can also set off asthma episodes.

Respiratory Infections

Any type of respiratory infection—such as a common cold or the flu—can trigger asthma symptoms. If you have asthma, it's especially important to take measures to stay well:

  • Wash your hands frequently
  • Don't touch your nose or mouth while you're out in public or around someone who's sick
  • Get a flu shot every year.

Less Common Asthma Triggers

Although these triggers are relatively uncommon, they are potentially serious for people who are sensitive to them.

  • Medications: A number of different medications are associated with asthma flare-ups, including pain medications (aspirin, ibuprofen, naproxen) and beta-blockers.
  • Food allergies: Some foods like fish, soy, eggs, wheat, and tree nuts are common food allergens. In some patients with life-threatening food allergies, eating these foods can also trigger asthma attacks, which can be deadly.
  • Exercise: Wheezing, coughing, and chest pain can occur in response to physical activity in people with asthma. This is known as exercise-induced bronchoconstriction (EIB) and is most common in teens and young adults.


The exact cause of asthma isn't well understood, but it's thought that a combination of genetic predisposition and exposures during life play a role. Asthma symptoms occur when an immune reaction causes airway constriction and excess mucus production, which together interfere with breathing.

Risk factors include a family history of asthma, exposure to tobacco smoke and other chemicals, dust, or fumes, and respiratory infections early in life. Many triggers can set off asthma symptoms, such as pollen, exercise, and food allergies.

There's no cure for asthma, but it can be managed. Identifying the triggers that cause you to have symptoms and, with the help of your healthcare provider, coming up with an asthma action plan that reduces your exposure to them, is key. Doing so may also reduce your need for medication.

Frequently Asked Questions

  • Does smoking cause asthma?

    Yes, smoking and exposure to cigarette smoke have been linked to the development of asthma at all ages. Asthma can develop in adults who smoke: In one large study, adult women smokers had a 40% higher risk of developing asthma.

  • Does air pollution cause asthma?

    Yes. Pollution is linked to developing asthma and experiencing worse asthma symptoms. Estimates suggest that 13% of children’s asthma is caused by traffic-related air pollution.

  • What is the most common cause of an asthma attack?

    The common cold is the most frequent cause of an asthma attack in both children and adults. In fact, asthma exacerbations that send people to the hospital are highest in the spring and autumn—at the height of cold season.

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Additional Reading

By Pat Bass, MD
Dr. Bass is a board-certified internist, pediatrician, and a Fellow of the American Academy of Pediatrics and the American College of Physicians.