A retropharyngeal abscess is caused by an infection with bacteria. Once the bacteria enter the tissue underneath the surface of the throat, the body forms a wall around the tissue in order to fight the infection. An abscess is filled with pus, which is made up of infected tissue and white blood cells.

The infection usually starts in the lymph nodes located in the neck, before spreading to the soft tissue in the back of the throat. The infection can also start in the tonsils, ears, or sinuses.

Group A beta-hemolytic streptococcus bacteria is the most common cause for the infection.