Sunburn

A sunburn is a medical condition in which overexposure of skin to the sun without any sort of protection leads to a reddish tint on the skin, as the skin is now "burned" by the sun.

Mainstream Smurfs Media
In the cartoon show episdoe "Mummy Dearest", Brainy suffered from sunburn when he is overexposed to the sun in Egypt, and thus had to be treated with swaddling cloths wrapped around him like a mummy.

Empath: The Luckiest Smurf stories
In the EMPATH: The Luckiest Smurf story series, sunburn is considered a serious condition among the Smurfs that causes their skin to turn reddish-purple, sometimes making them be mistaken for a Purple Smurf.