i get the rash too. i have narrowed it down to the aluminum ingredient that is part of the antiperspirant in most deodorant/antiperspirants out there on the market. i can use just deodorant sticks/gels without much problem, and i currently use Toms. however, i notice this only lasts half of the day, and i do stink when i exercise and ride hard. i think i am going to switch over to isopropyl and see how that works. do you use it once in the morning, or do you apply throughout the day? thanks, this has been very interesting and informative!