<prompt> Toxic epidermal necrolysis TEN involves body surface area1010-2020-3030  <response>: Based on body surface area BSA of skin involved, epidermal necrolysis is classified into SJS: less than 10 BSASJS_TEN overlap: 10-30 BSA TEN : more than 30 BSA. From illustrated synopsis of dermatology and sexually transmitted diseases neena khanna 5th edition page no 92 