Here is a study done in the late 80's that showed the increase propensity for scrotal skin to cause more DHT conversion.
Androgen therapy of hypogonadal men with transscrotal testosterone systems
The American Journal of Medicine
Volume 83, Issue 3 , Pages 471-478, September 1987
Abstract
The need for improved controlled delivery of testosterone to hypogonadal men stimulated the development of a self-adherent transscrotal testosterone system to provide programmed testosterone delivery through the uniquely permeable scrotal skin. In this short- and long-term efficacy trial, the responses of testosterone and its metabolites to the application of transscrotal testosterone systems of varying testosterone content were compared with the response to 200 mg of testosterone enanthate. Daily transscrotal testosterone system administration resulted in a rapid increase of testosterone and bioavailable, nonsex hormone binding globulin-bound testosterone levels to normal, peaking at two hours, followed by a slow decline over 23 hours, resembling the diurnal variation of endogenous testosterone. One year of daily transscrotal testosterone system therapy demonstrated continued reliable absorption of testosterone and suppression to normal of the luteinizing hormone in two of three patients. There was a greatly disproportionate increase of serum dihydrotestosterone (DHT) over testosterone, suggesting 5-alpha reduction at the scrotal site. The subjects reported marked subjective improvement. Thus, the transscrotal testosterone system is a novel, effective, and well-tolerated method of delivering testosterone to hypogonadal patients.
