Second degree sunburns can last anywhere from 10 to 21 days. The exact length of time varies depending on the person and the medical treatment used.
Burns are classified according to how deep the burn goes through the tissue layers. Second degree burns affect the entire epidermis and upper layers of the dermis. Since more damage is caused with second degree burns than those of first degree burns, the healing time is quite longer.
Some second degree sunburns require grafting and other forms of medical treatment in order to heal properly and minimize scarring. According to the University of New Mexico Hospital, a doctor should be consulted concerning a second degree burn of any kind.