Risk Factors

Most cases of asthma start during childhood as the immune system matures. Certain genetic and other risk factors may increase the risk of developing asthma. For example, exposure to allergens, irritants, and infections is linked to the onset of asthma symptoms.

It is often hard to avoid exposures that cause asthma symptoms. Talk to your doctor about what triggers your symptoms. They can suggest lifestyle changes or other ways to reduce your risk of asthma symptoms.

What are possible triggers of asthma?

Common triggers of asthma and wheezing are allergens, irritants, and air pollutants, such as:1

  • Dust mites
  • Cockroaches
  • Pet dander (dead flakes of skin that are shed by your pet)
  • Pollen (powdery substance released by plants that travel by the wind)
  • Mold

People with asthma can experience symptoms from many kinds of triggers, such as:1

Are there genetic risk factors of asthma?

Family history of asthma is a main risk factor for asthma. For example, people with a parent with asthma are 3 to 6 times more likely to develop asthma.2

This means there is a genetic element to asthma development. Researchers have identified mutations in many genes that may be linked to asthma or wheezing. However, we do not yet understand what the most important genes are and their specific roles.3,4

What are other risk factors for asthma?

Viral infections

Viral infections are an important risk factor for asthma. Several studies have shown links between infections during childhood and development of asthma symptoms. For example, infections before age 3 are linked to wheezing by 6 years old. The most common viruses that cause respiratory infections in children include:4,5

  • Human rhinoviruses (HRVs)
  • Respiratory syncytial virus (RSV)
  • Influenza
  • Coronaviruses

We do not yet know why viral infections are linked to asthma development. One theory is that viruses make airway inflammation worse.4

Allergies

Asthma and allergies are closely related, and allergies are a main risk factor for asthma. When your immune system mistakes an allergen for a threat, it releases chemicals that lead to symptoms of allergies. For some people, this reaction also affects the lungs and airways, causing asthma symptoms. Common allergens that trigger asthma include:4-6

  • Pollen
  • Dust mites
  • Mold spores
  • Pet dander

Work exposures

Your work environment is a potential risk factor for asthma symptoms. If you have asthma, exposure to irritants in the workplace can cause symptoms. Exposure at work can also cause asthma to develop for the first time.2,4

When work exposures go unrecognized, asthma can progress further and have worse symptoms. A careful history of work-related exposures is important to identify causes of asthma. Common work-related exposures linked to asthma symptoms include:2

  • Industrial dusts
  • Wood dusts
  • Chemical fumes
  • Vapors
  • Molds

Smoking

Studies have found a link between active smoking and asthma. Asthma symptoms are also harder to control in smokers than nonsmokers. Experts have shown that smoking increases airway irritation and inflammation, leading to asthma.3,4

Several studies have also shown a link between secondhand smoke exposure and asthma. This includes children exposed to smoke in the womb. It also includes children who grow up in homes with smokers. Childhood exposure to secondhand smoke is linked to a higher risk of developing asthma as an adult.3,4

Air pollution

Exposure to outdoor and indoor air pollution is another risk factor. Children who live in urban areas have a higher risk for asthma. This may be because urban areas have higher levels of pest allergens and indoor pollutants.4

Urban homes have twice as much particulate matter than non-urban homes. This is the mixture of solid and liquid particles in the air, such as dust and smoke. Indoor sources of particulate matter include smoking, sweeping, and stove use. Indoor exposure to particulate matter is linked to more asthma symptoms in urban homes.4

Nutritional factors

Children and adults who are overweight or obese have a higher risk of asthma. People who are overweight with asthma also have worse symptoms, more healthcare usage, and lower quality of life. We do not yet know how body weight is linked to asthma severity. One theory is that higher inflammation caused by obesity may lead to airway problems.2,4

Certain vitamins and nutrients may also play a role in developing asthma. For example, low levels of folate and vitamin D are associated with asthma in children.4

Hygiene hypothesis

The “hygiene hypothesis” is a concept that may explain why asthma has become the most common chronic disease in many developed countries. Over the past several decades, we have seen higher antibiotic use, better hygiene, and more urbanization. This has reduced exposure to certain germs. Very clean environments may not give the immune system the chance to mature. Instead, the immune system contributes to the development of asthma.7

So far, the hygiene hypothesis is supported based on some studies. We need more research to know how cleanliness is linked to asthma.

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Written by: Matt Zajac │Last reviewed: September 2021