Though this is only anecdotal, some of the people posting about hair loss with WEN mentioned having virgin hair, not chemically processed at all, no coloring or dyes, etc. When they switched products the problem went away and their hair eventually grew back. There must be sensitivity to the ingredients. I'd suspect that whatever ingredient it is, must be something not often used in other hair care products. Which makes me suspect the menthol, for one. Could be a bunch of other things. The only thing I can say for sure, is that my hair loss was quite severe with WEN. Usually my hairdresser could hide my hair loss when she cut my hair…. but there grew a point where she couldn't, and it looked thin even with her being the miracle worker that she is. It was definitely at its worst using WEN. When I switched hair products (to b.s. and acv) she said my hair looked thicker. And now not straightening my hair any longer and being CG, it looks even thicker now.