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Bronchioles are small airways that connect your airways (bronchi) to tiny air sacs of the lung. When these small airways swell, it is called bronchiolitis.

Key Facts

  • Infants younger than 3 months of age are at greatest risk of getting bronchiolitis.
  • Bronchiolitis is caused by a viral infection and can almost always be treated at home.
  • It usually takes about 2 or 3 weeks for the infection to go away.
  • A small percentage of children develop a more serious illness that requires hospitalization.

How Bronchiolitis Affects Your Body

Bronchiolitis develops when an infection causes the very small airways in the lungs (the bronchioles) to become swollen and filled with mucus. This makes it hard to get air into the lungs, which may result in shortness of breath and coughing. A second type of bronchiolitis, called bronchiolitis obliterans, is a rare and dangerous condition seen primarily in adults.

What Causes Bronchiolitis?

Bronchiolitis is almost always the result of a viral infection. Many infections could lead to bronchiolitis, though the most common culprit is respiratory syncytial virus (RSV). The viruses that cause bronchiolitis are highly contagious, and outbreaks typically occur in the winter.

Who Is at Risk?

Infants, especially those under 3 months old are at the greatest risk because their lungs and immune system are not fully developed. Other factors that may make a child more susceptible include:

  • Premature birth
  • Underlying health conditions, especially heart and lung-related
  • Exposure to tobacco smoke
  • Contact with other children who are sick, such as in child care settings

Reviewed and approved by the American Lung Association Scientific and Medical Editorial Review Panel.

Page last updated: March 6, 2020

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