Scarlet fever, sometimes known as scarlatina, is an infection caused by the bacteria Streptococcus pyogenes. It is usually diagnosed on the non-specific signs and symptoms including sore throat, fever, headache, tiredness, nausea and vomiting, which are then followed after 24 hours or so by the appearance of a distinctive rash on the abdomen and chest. This is red and blanching (goes white when pressed) and more pronounced in the skin folds, for example, the neck, armpits, groin, elbows and knees. The face may be flushed, the inside of the mouth spotty, and the tongue initially covered with a white coat which subsequently disappears, leaving it with a red and inflamed appearance.

Scarlet fever is highly contagious and can cause life-threatening conditions such as shock. It is much more likely to affect children than adults, seems to peak in spring and autumn, and although it is much less common than it used to be, there are still several thousand cases reported each year. Most cases are mild and self-limiting, getting better within a week in most cases, but prompt antibiotic treatment significantly reduces the risk of complications.