Coughing up thick, green mucus may mean a bacterial or, less often, viral infection, but that's not always true. You ...

Green mucus results from an intensified immune response. The green tint comes from an enzyme called myeloperoxidase, which is produced by neutrophils (a type of white blood cell). This enzyme ...

If your mucus is gray or black... …you likely inhaled dark-colored particles, like smoke from a fire or heavy exhaust. Regular smokers can also blow out darker ...