If a blistering burn covers 20% or more of the body (a child's whole back), seek medical attention. Anyone with a sunburn who is suffering fevers and chills should also seek medical help, he says. Finally: consider the burn a warning that your sun-safety net has failed and vow to do better. That means using sunscreen, covering up with clothing and hats and avoiding the sun as much as possible between 10:00 and 16:00.