Scarlet fever is simply a rash that develops in conjunction with strep throat, a bacterial infection. It most commonly turns up in children between 4 and 8. The rash looks and feels rough, like sandpaper, and usually starts on the upper body and spreads outward. Scarlet fever is very common and easily treated with penicillin (the same meds used to treat strep).
Many people confuse the term scarlet fever with rheumatic fever, a heart disease that can strike when strep throat goes untreated. It was more common in the past, before there was widespread access to antibiotics. It was actually rheumatic fever, not scarlet fever, that used to cause blindness and even death (remember Little Women?). These days, we treat scarlet fever and strep with antibiotics, and it is important to use them exactly as prescribed by your doctor to avoid any complications.