What: Gives hair that smooth feeling after conditioning. It's a silicone-based polymer that's used to seal in moisture. It also protects the hair follicle from heat and provides shine and gloss. Health effects: Because it seals in moisture and seals out everything else, it doesn't let hair breathe and can lead to hair thinning. The alternative: Natural oils such as jojoba, argan, rose hip, sweet almond, olive oil or shea butter.