Scarlet fever is an infection caused by Group A Streptococcus ("strep") bacteria. It causes a finely textured rash that can appear like sandpaper along with other symptoms. It usually occurs after a strep infection of the throat (strep pharyngitis, or strep throat), but occasionally after a strep skin infection. The rash of scarlet fever is caused by a toxin that the strep bacteria produce.
Scarlet fever once was common among children ages 2 to 10, but now it is relatively rare. The reason for this remains a mystery, especially because there has been no decrease in the number of cases of strep throat or strep skin infections.