Specific signs and symptoms of diphtheria depend on the particular strain of bacteria involved, and the site of the body affected. One type of diphtheria, more common in the tropics, causes skin ulcers rather than respiratory infection. These atypical cases are usually less serious than the classic cases, first described by Hippocrates, that lead to severe illness and sometimes death.

The classic case of diphtheria is an upper respiratory infection caused by toxin-producing bacteria that leads to the creation of a gray pseudomembrane over the lining of the nose/throat, around the area of the tonsils. This pseudomembrane may also be greenish or blueish, and even black if there has been bleeding. 

Early features of the infection, occurring prior to the appearance of the nasopharyngeal pseudomembrane, include:
-- Fever (though not usually a very high temperature), malaise and weakness
-- Enlarged lymph nodes at the front of the neck (popularly referred to 'swollen glands')
-- Swelling of soft tissue in the neck (giving a 'bull neck' appearance)
-- High heart rate (tachycardia, disproportionately high for the level of fever).

Children with a pharyngeal diphtheria infection are more likely to have the following early features:
-- Nausea and vomiting
-- Chills, headache and fever.

After a person is first infected with the bacteria there is an average incubation period of 5 days before early signs and symptoms appear. This 'prodromal period' lasts between 12 and 24 hours and, if the bacteria colonizing the nasopharynx are toxic, a pseudomembrane forms over the following 2-3 days, leading to:
-- Sore throat
-- Difficulty swallowing (dysphagia)
-- Possible obstruction that causes difficulty breathing (shortness of breath - dyspnea).