Causes and Risk Factors of Asthma

As common as it is, what causes asthma isn't fully understood. It's likely there is a genetic component that predisposes a person to developing 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 pathophysiology of asthma symptoms—bronchoconstriction (narrowing of the bronchi, or airways) and excess mucus production that impede airflow.

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

Inhaling through nebulizer at doctor's office!
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Risk Factors

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

  • Have a family history of asthma
  • Had a viral respiratory infection as a baby or young child
  • Have allergies, such as hay fever (allergic rhinitis) or eczema (atopic dermatitis)
  • Are exposed to dust or chemical fumes in your work
  • Smoke or have ever smoked cigarettes, 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 or obese—people with asthma who are obese often have worse symptoms and less effective control of their condition

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 allergens is compromised in children with eczema, allowing them to become sensitized to antigens.

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, both indoors and outdoors, and many people have more than one.

Indoor Triggers

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

  • Dust mites: Dust mites (Dermatophagoides pteronyssinus) are microsopic arthropods 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. 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. Pollens from many different kinds of grasses, weeds, and trees may trigger allergy symptoms.
  • 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.

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, and get a flu shot every year.

Less Common Asthma Triggers

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

  • Medication: A number of different medications are associated with asthma, among them pain medications (aspirin, ibuprofen, naproxen) and beta blockers.
  • Foods: Certain foods, including fish, soy, eggs, wheat, and tree nuts, are known to trigger asthma, especially in infants and children.
  • Exercise: Wheezing, coughing, and chest pain that occur in response to physical activity, known as exercise-induced asthma (EIA), is thought to occur because people tend to breathe through their mouths during exercise, which sends cold, dry air to the lungs. (Air is warmed and moisturized when inhaled through the nose).

Genetics

It is well-established that asthma runs in families, a sure sign 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.

A Word From Verywell

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 doctor, coming up with an asthma action plan that includes mitigating your exposure to them, is key. Doing so may also reduce your need for medication.

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