Every day. I know I shouldn't, but if i skip even one shampoo, my hair gets greasy halfway into the second day. There's nothing worse than that for me.
I've never heard that it gets thinner, but much drier and more brittle and damaged. especially if you use a poo that contains sulfates. I usually wash mine every 3 days, but I wet and condition it almost every day. I've been using VO5, but I'm going to be switching to activate (sulfate free). Plus there is always the no-poo method of cleaning your hair if you have hair that is curly or tends to be on the dry side! ~~jax
I don't think washing your hair with regular shampoo or even just water too often is good, but I still do it quite often, absolutely after working out, I hate the smell of sweaty hair :yuck2:
I stopped using regular shampoo though, only all natural organic shampoos & conditioners that contains no crap like sulfates and chemicals that only hurt your hair.
everyday, becase its humid here in the Philippines and not to mention the pollution. But I just shampoo my hair trice a week but using conditioner everyday.