A little protein that you rinse out of your hair is no big deal. There is so little of the protein in there, and it's usually just put in the product for show, anyway. I don't think there is anything for you to worry about, especially since you are rinsing it out, the protein just goes down the drain, anyway. And a little protein in a leave-in is fine too, because it's usually listed really far down on the ingredients list, often after fragrance and preservatives, which means there's hardly any of it in the product anyway, and again, it's often in there as a marketing gimmick more than it actually does anything anyway.

To be honest, though I know many people swear by protein conditioners, there doesn't seem to be too much they can do to help damaged hair. Since hair is dead, it's more like a fabric-- like a wool sweater. Soaking your hair in protein is like covering a sweater in yarn. The sweater, and our hair, have no way to make use of the protein (or yarn) to heal itself (living tissues often can use things to repair themselves, but dead things can't). Nothing repairs hair, I hate to say, so the protein functions more as a moisturizer.

There has been some research to show protein can help somewhat strengthen hair that's been damaged, but I'm not sure how much it can really strengthen our hair. True, I am really skeptical by nature, so it's best to assume they can't strengthen our hair much, so we err on the side of protecting our hair instead of counting on proteins to undo any damage. Also, strengthen is not the same as repairing damaged hair. So I wouldn't rely on protein alone to solve hair issues, or to feel it's now okay to do damaging things to our hair because protein treatments will reverse the damage, because they can't.

For more information, you can check out the Ingredients Dictionary or click on protein, or another popular form of protein often used, keratin.