Part of Strep. Scarlet fever is produced by the breakdown if you will of the strep bacteria. Not everyone who has "strep" develops the rash. The scarlet fever rash is more common in children. If you suspect you have a strep infection, seek treatment asap in order to avoid complications.
Early Dx & Rx. Estimates suggest it takes about 12-18 hrs after you acquire a rash producing strain of strep for the germ to begin producing the toxin that causes the rash. Early detection (family or exposed) can permit early rx and stop the rash. The rash itself is of minimal importance. The goal of rx (within 1st 9 days of sx) is to stop antibody production leading to rheumatic fever & spread to others.