A type of bacteria called Corynebacterium diphtheria causes diphtheria. The condition is typically spread through person-to-person contact or through contact with objects that have the bacteria on them, such as a cup or used tissue. You may also get diphtheria if you’re around an infected person when they sneeze, cough, or blow their nose. Even if an infected person doesn’t show any signs or symptoms of diphtheria, they’re still able to transmit the bacterial infection for up to six weeks after the initial infection.

The bacteria most commonly infect your nose and throat. Once you’re infected, the bacteria release dangerous substances called toxins. The toxins spread through your bloodstream and often cause a thick, gray coating to form in the:
-- nose
-- throat
-- tongue
-- airway

In some cases, these toxins can also damage other organs, including the heart, brain and kidneys. This can lead to potentially life-threatening complications, such as myocarditis, paralysis, or kidney failure.