I'm sorry, but if your body is reacting to something in the form of a rash, it is telling you to discontinue usage. This rash is your body's way of rejecting something and screaming to you to stop.
I know yall love yall some BT and all, but if you are allergic please just stop. It's not that serious to neglect your health over a growth aide or to walk around with dark patches on the back of your neck. I would discontinue use ASAP. Your hair will grow regardless, maybe a little slower, but it will grow. Just take care of it the good old fashion way, and I promise you you won't be dissapointed.