You won't have thinner hair from one good massage, so stylists can do it without problem because it won't have long-term repercussions. But if you're massaging very vigorously over an extended period of time (months) as you would in a co-washing regimen you could experience hair loss. I think it also has to do w/ overconditioned hair follicles... so it's the massages combined w/ the softened follicles.