Sunburn

A 14-year-old boy is brought to the office for the evaluation of a sunburn. He had just returned from a week-long vacation to Florida, where his activities included swimming in the ocean, playing football at the shore, and river rafting. On the 2nd day, he started developing painful redness on his extremities and face, after which he began applying sunscreen before going out in the sun. His condition did not improve, and his skin started peeling off and developing blisters in the affected areas by the 4th day. The patient is otherwise healthy and takes no medications. Vitals are within normal limits. Physical examination shows a fair-skinned adolescent with tender, blanching erythema and blisters on his shoulder and extremities as shown:  


<sup>Reproduced from: ">Wikimedia Commons   

Reproduced from: ">Wikimedia Commons</sup>  
Which of the following is the most likely diagnosis?