RAC1 and Stevens-Johnson syndrome: It is known that massive keratinocyte apoptosis as a result of severe allergic drug reactions causes a similar epidermal detachment, for example, in Stevens-Johnson syndrome or Toxic epidermal necrolysis.40, 41 Hence, it is well conceivable that the increased UV-light-induced keratinocyte apoptosis in Rac1-EKO mice is the cause for both the epidermal detachment and the skin-erosions observed in long-term UV-irradiation studies.