Erythema toxicum neonatorum
Erythema toxicum neonatorum is the medical name for this condition. "Normal newborn rash" is the name we use when talking to families about it. There is nothing toxic or concerning about this rash. More than 50% of newborns have it in the first few days of life; it causes no discomfort and resolves without treatment. Reassurance and anticipatory guidance about the shifting location of the lesions (which can make it appear to be spreading/worsening) is all that is required.