The lining of your respiratory system, extending from your nose through the airways of your lungs, is coated with mucus. This clear, sticky substance helps keep the airways clean by capturing particles and chemicals from the air you breathe. Environmental particles or infectious agents can cause the normally clear mucus to appear black or tinged with black streaks. Depending on the cause, black mucus can be inconsequential or an indication of a serious medical problem.
Dirt and Dust
It has almost certainly happened to you at some point -- you blow your nose and notice the fluid in your tissue looks black. The most common cause of gray or black mucus is dirt and dust. When you are working in the garden, cleaning a dusty attic or doing some other dirty job, tiny dirt and dust particles are stirred into the air. As you breathe these particles in, they stick to the respiratory mucus and are subsequently expelled when you blow your nose or cough.
Smoke
Inhaling smoke can cause black mucus. Although cigarette smoking more typically turns the mucus brown, it can also be tinged black. Smoking marijuana can also cause black mucus or phlegm. The black coloration is likely due, at least in part, to the high aluminum content of both tobacco and marijuana smoke. Black mucus associated with inhaling smoke from a fire may indicate a serious inhalation injury and is considered a medical emergency.
Environmental Hazards
Miners, especially coal miners, can have black mucus due to inhalation of coal or graphite particles. Chronic exposure may lead to black lung disease, also known as coal workers’ pneumoconiosis. Other types of workers exposed to inhaled environmental pollutants such as beryllium may also experience black mucus. Protective gear such as masks and respirators help filter the air and decrease the burden of environmental particles on the lungs.
Infections
Specific types of chronic sinusitis and pneumonia can cause black mucus. Two examples are mucormycosis and aspergillosis. These serious fungal infections are uncommon and are typically seen only in people with a compromised immune system.
Foreign Bodies
With their insatiable curiosity, children rather commonly put objects in their noses and mouths. These objects -- called foreign bodies -- can become lodged in the upper recesses of the nose or in the airways. Left undetected, foreign bodies can cause infections or erode into other structures, which may lead to black drainage from the nose or black phlegm being coughed up from the lungs.
Warning
If you have black mucus with no obvious cause, see your doctor as soon as possible to determine the cause and appropriate treatment. Seek immediate medical attention if the mucus is accompanied by a fever, chills or difficulty breathing.