A mild sunburn typically lasts for three to five days, according to Dr. Alan Greene. A moderate to severe sunburn can last several days longer. Symptoms of sunburn are typically noticed around 6 hours after sun exposure, and reach their peak about 24 hours later.
In some cases, a serious sunburn can result in blistering, nausea, chills, fever, heat stroke and dehydration, according to Dr. Greene. While the visible effects of a sunburn may dissipate in a few days, the effects of radiation damage on the body are much longer lasting. Sun exposure increases the risk of premature aging, skin lesions and skin cancers.