Britannica Sources used in this answer

Why can nitrogen oxide exposure cause breathing symptoms hours after exposure?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — respiratory disease The bronchioles of the lungs are the site where oxygen is exchanged for carbon dioxide during the process of respiration. Inflammation, infection, or obstruction of the bronchioles is often associated with acute or chronic respiratory disease, including bronchiectasis, pneumonia, and lung abscesses.

Exposure to oxides of nitrogen, such as nitrogen dioxide, is characteristically not followed by immediate symptoms. Instead, respiratory symptoms—including a cough and progressive shortness of breath—typically develop several hours after the initial exposure.1

This delayed onset occurs because the exposure triggers an acute inflammation of the small airways known as bronchiolitis. When individuals inhale these gases—which may occur in environments such as silos, during welding in enclosed spaces, or in fires involving plastic materials—the resulting inflammatory damage to the lung tissue manifests over time rather than instantaneously. A chest radiograph in such cases typically reveals patchy inflammatory changes consistent with this condition. It is important to note that even when symptomatic recovery occurs, it may mask an incomplete resolution of the underlying inflammation.1