A very wide range of diseases or toxic substances, including some drugs, can cause ARDS. They include:

• Breathing in (aspiration) of the stomach contents when regurgitated, or salt water or fresh water from nearly drowning.
• Inhaling smoke, as in a fire; toxic materials in the air, such as ammonia or hydrocarbons; or too much oxygen, which itself can injure the lungs.
• Infection by a virus or bacterium, or sepsis, a widespread infection that gets into the blood.
• Massive trauma, with severe injury to any part of the body.
• Shock with persistently low blood pressure may not in itself cause ARDS, but it can be an important factor.
• A blood clotting disorder called disseminated intravascular coagulation, in which blood clots form in vessels throughout the body, including the lungs.
• A large amount of fat entering the circulation and traveling to the lungs, where it lodges in small blood vessels, injuring the cells lining the vessel walls.
• An overdose of a narcotic drug, a sedative, or, rarely, aspirin.
• Inflammation of the pancreas (pancreatitis), when blood proteins, called enzymes, pass to the lungs and injure lung cells.
• Severe burn injury.
• Injury of the brain, or bleeding into the brain, from any cause may be a factor in ARDS for reasons that are not clear. Convulsions also may cause some cases.

Usually ARDS develops within one to two days of the original illness or injury. The person begins to take rapid but shallow breaths. The doctor who listens to the patient's chest with a stethoscope may hear "crackling" or wheezing sounds. The low blood oxygen content may cause the skin to appear mottled or even blue. As fluid continues to fill the breathing sacs, the patient may have great trouble breathing, take very rapid breaths, and gasp for air.