Diphtheria is a bacterial disease caused by Corynebacterium diphtheriae. The infection commonly affects the throat and may lead to obstruction of the airways and death. Exotoxin-induced damage occurs on organs such as the heart. Nasal diphtheria may be mild, and chronic carriage of the organism frequently occurs; asymptomatic infections are common. Transmission occurs from person to person, through droplets and close physical contact, and is increased in overcrowded and poor socioeconomic conditions. A cutaneous form of diphtheria is common in tropical countries and may be important in transmission of the infection.