Basically the two diseases are the same.
Scarlet fever differs from streptococcal sore throat chiefly by the presence of a red skin rash.
Scarlet fever is an illness that usually begins abruptly, from one to three days following exposure, with headache, fever, sore throat, and vomiting. The skin will feel hot and dry. The entire tongue will gradually become red. A day or two later, small flat red points will make their appearance on the neck and chest and will gradually spread over the body. Often the skin between the flat red points will also take on a bright red flush.