Pollutants, infections, and lung cancer may cause black mucus ... or smoke — for a short period will notice that their mucus returns to a regular color once exposure to the pollutants stops.

Serious conditions that may cause you to cough blood are lung cancer ... blood-stained phlegm that is thick and dry in consistency. This phlegm may be yellow, green, or brown in color.

Coughing up blood, medically known as hemoptysis, involves coughing or spitting up blood or blood-streaked mucus ... clot in the lung), or medications like blood thinners. In some cases, coughing up ...