Acute lung injury often comes on suddenly, so the first signs are usually rapid breathing, a feeling of “air hunger,” and a cough that may bring up frothy or pink-tinged sputum. Many people or their families notice severe shortness of breath that worsens over minutes to hours, sometimes after a trigger like pneumonia, sepsis, major trauma, or inhaling smoke or chemicals, along with bluish lips or fingertips and marked fatigue. In hospitals, doctors often first recognize it by a sharp drop in blood oxygen levels despite extra oxygen, crackling sounds in the lungs on exam, and new hazy areas on a chest X-ray; anyone with these warning signs needs urgent care.