How do you know its the deca? You started this deca and test all at once? If so, it could be either. I would try pulling the deca out first and see if you get relief. If not, I would stop both. If this is a new brand, theres a chance you are allergic to one of the solvents ORRR there is an equal chance that the hives have nothing to do with the gear. It could be something outside of that. One way you could test this out and see if you get relief from Benadryl, then we can be certain that you are suffering an allergy of some sort best from your cycle or from something else in your environment.