The idea here is that without lots of bloodwork and test no one will ever know for sure if it makes a difference on the overall effect if you mix the two. For me the welts were enough of an issue, however small, that just pinning seperate made sense. But why ever risk it with mixing? These are aminos tied together, what if mixing them even if for a few minutes sometimes mixes up those amino chains... Its a chance I'm just not willing to take. I work hard, for me, for my money so I want the best results possible. So if I don't mix the peps, buy from a source where i know purity is 98+% then I know I'm getting the best I can get from what I have. And I don't have red welts...LOL.