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What Causes Asthma?

The exact cause of asthma isn't known. Researchers think some genetic and environmental factors interact to cause asthma, most often early in life. These factors include:

  • An inherited tendency to develop allergies, called atopy (AT-o-pe)
  • Parents who have asthma
  • Certain respiratory infections during childhood
  • Contact with some airborne allergens or exposure to some viral infections in infancy or in early childhood when the immune system is developing

If asthma or atopy runs in your family, exposure to irritants (for example, tobacco smoke) might make your airways more reactive to substances in the air.

Some factors might be more likely to cause asthma in certain people than in others. Researchers continue to explore what causes asthma.

The Hygiene Hypothesis

One theory researchers have for what causes asthma is called the hygiene hypothesis. They believe that our Western lifestyle—with its emphasis on hygiene and sanitation—has resulted in changes in our living conditions and an overall decline in infections in early childhood.

Many young children no longer have the same types of environmental exposures and infections as children did in the past. This affects the way that young children's immune systems develop during very early childhood, and it may increase their risk for atopy and asthma. This is especially true for children who have close family members with one or both of these conditions.

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Living With and Managing Asthma


Asthma Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Asthma, visit www.clinicaltrials.gov.

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Visit Children and Clinical Studies to hear experts, parents, and children talk about their experiences with clinical research


Asthma in the News

September 13, 2012
No significant difference in asthma control across three approaches to adjust medication dose in mild asthma
A study comparing three common approaches to periodically adjust the dosage of inhaled corticosteroids (ICS) for people with mild asthma has found no detectable differences in how often a person’s asthma worsened. The methods examined in this study were a patient-guided modification based on symptoms, an assessment made by an examining physician, or the results of a breath test to measure inflammation.

View all Asthma Press Releases

 
June 15, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.

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