Heard of "toasted skin" syndrome? What is it? Toasted skin syndrome describes the type of sunburn that resembles the burn on a piece of toast—also described by some as a red fishnet pattern. The medical term is erythema ab igne, and it occurs when the skin is exposed to low levels of heat over a sustained period. A common cause of this short-term rash rises from hugging a hot water bottle to your bare skin. Experts say that there are no long-term effects, so long as the skin is not exposed to continual heat. If you are a hot water bottle enthusiast, try wrapping the bottle in a cloth layer to avoid direct heat to the skin.