Diphtheria is an infection that may cause a lung or skin infection. Some people may not be sick from it but may carry the germ that causes the infection. It mainly infects the mouth, throat, and nose. It can also affect your skin and other body parts. You can become sick if you breathe the air after a person with the infection sneezes, coughs, or speaks. You can also get the infection by touching things that an infected person has handled. Treatment helps keep the infection from spreading in the body.