Chemical pneumonitis is inflammation of the lungs or breathing difficulty due to inhaling chemical fumes, or aspirating (breathing in and choking on) gastric acid from the stomach, mineral oil, gasoline, or other damaging chemicals.

Many household and industrial chemicals are capable of producing both an acute and a chronic form of inflammation in the lungs. Acute chemical pneumonitis causes swelling of the lung tissue, movement of fluid into the air spaces in the lung, and less ability to absorb oxygen and get rid of carbon dioxide. In severe cases, death may result from lack of oxygen reaching the tissues (hypoxia).

Some of the most common dangerous, inhaled substances include:

• Chlorine gas (during use of cleaning materials such as chlorine bleach, in industrial accidents, or near swimming pools)
• Grain and fertilizer dust
• Noxious fumes from smelting, welding, or other metal work and the production of solvents and pesticides
• Smoke (from house fires and wildfires)

Chronic chemical pneumonitis can occur after only low levels of exposure to the irritant over extended periods of time. This causes inflammation and may bring on fibrosis (scarring) which decreases the ability of the lungs to get oxygen to the body and release carbon dioxide as waste, and stiffening of the lung. Unchecked, this condition may ultimately lead to respiratory failure and death.