Although most cases of influenza (flu) get better without causing other problems, complications sometimes develop.
Possible problems from the flu include:
- Pneumonia, which is an infection of the lungs. It can be serious in older adults, people who have other health conditions, and in people who are pregnant.
- Bronchiolitis. This is an inflammation of the small airways. It affects infants and can cause a serious lower respiratory infection.
- Sinusitis. This means the mucous membranes that line the inside of the nose and facial sinuses become infected and inflamed.
- Croup. Croup is a swelling or blockage in the windpipe. It causes hoarseness, a barking cough, a high-pitched sound when breathing in, and trouble breathing.
- Worsening symptoms from chronic obstructive pulmonary disease (COPD) or other lung conditions.
- Inflammation of the heart muscle, the sac around the heart, or other muscles in the body.
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Current as of: February 27, 2026
Author:
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