This blog post contains affiliate links. Please read disclaimer.   Sometimes a tiny letter can make a huge difference. Make you question things, for example. In cosmetic science, that letter is usually a “v”. Why a “v” you ask? And imagine how great it would have been had I said a “y” -Y a “y”? Because “in vivo” sounds pretty similar to “in vitro”, but in terms of results there is a huge difference.     See, many ingredients proove their claim on human cells. In the lab, in petri…