I thought i posted already but I can't find my post. Anyway, I've been cowashing for 4 months and it has thinned out my hair very noticeably. I think it may have something to do w/ the manual friction of cowashing combined with the softening of the roots from the conditioner. But it could be other things as well, like my scalp not agreeing with a particular ingredient in the cowash I've been using. I think the thinning is caused by excess shedding. I stopped cowashing and have been low-pooing and already I'm seeing SIGNIFICANTLY less shedding in the shower.
I can't offer a lot of advice as I newly realized how much it has thinned my hair, and I'm also trying to figure out myself. But I feel ya.
This is my thread: bad news - cowashing is thinning my hair!
You might want to look into this also>
Excessive Shedding: Could Co-Washing Be the Culprit? | hairscapades