Asthma Causes and Triggers

What causes asthma?

The exact causes for developing asthma are unknown and may be different from person to person. However, asthma can also occur when the body’s natural defenses against germs and sickness react strongly to a new substance in the lungs.

Asthma usually starts during childhood when the body’s defense system is still taking shape. However some people don’t show signs of asthma until adulthood — this is known as adult- onset asthma. Certain factors can affect how your lungs develop or how your body fights germs.

 Many factors may work together to cause you to develop asthma, such as:

  • Things in the environment (called allergens) that affected you as a baby or young child, including cigarette smoke or certain germs
  • Viral infections that affect breathing
  • Family history, such as a parent who has asthma (especially your mother) The following may also raise the risk of developing asthma.

The following may also raise the risk of developing asthma:

  • Allergies: Asthma is usually a type of allergic reaction. People who have asthma often have other types of allergies, such as food or pollen allergies.
  • Obesity: Being overweight can raise your risk of developing asthma or make your asthma symptoms worse.
  • Race or ethnicity: Puerto Rican people and Black or African American people have a higher risk of developing asthma than people of other racial or ethnic groups. Black or African American and Hispanic children are more likely than non-Hispanic White children to die from asthma.
  • Sex: More boys than girls have asthma as children. In adults, asthma is more common among women.
  • Occupational hazards: Breathing in chemicals or industrial dust in the workplace can raise your risk of developing asthma.
  • Climate change: Air pollution and changing weather patterns contribute to asthma onset and exposure to allergens.

Asthma in Our Communities fact sheet
Fact sheet
Asthma in Our Communities

Learn how asthma affects people from some communities more than others and steps for managing asthma.

How asthma affects the lungs

Normally, the body’s natural defense system helps fight infections. But it may also respond to things you breathe in, such as pollen or mold. In some people, the defense system reacts strongly by creating  inflammation . The airways may also become too sensitive, or hyperresponsive, and narrow too much when you breathe in something that is usually harmless. 

When this happens, the airways swell, narrow, and can create more mucus. The muscles around the airways may also tighten. This can make it even harder to breathe. Over time, the airway walls can become thicker.

To understand asthma, it helps to learn how the lungs work.

Can I prevent asthma?

Because the exact cause is unknown, you may not be able to prevent asthma in yourself or your children.

However, you can take steps to help prevent asthma from developing. They include doing your best to keep your home free of dampness and mold, avoiding air pollution as much as possible, and making a healthy lifestyle a priority for you and your family, for example, by adding more fruits and vegetables to your diet.

Research for your health

NHLBI-supported research on asthma has led to more and better treatment options to improve the health of people who have asthma. Through our current research, we hope to better understand how our genes and the environment we live in affect our risk for developing asthma.

Asthma triggers

Asthma triggers are things that set off or make asthma symptoms worse. Common triggers include:

  • Indoor allergens, such as dust mites, mold, and pet dander or fur
  • Outdoor allergens, such as pollens and mold
  • Emotional stress
  • Physical activity, although with treatment you or your child should still be able to stay active
  • Infections, such as colds, the flu, or COVID-19
  • Certain medicines, such as aspirin, which may cause serious breathing problems in people with asthma that is difficult to treat
  • Poor air quality or very cold air

Learn about avoiding triggers to help manage your asthma.

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