Silicones are tricky. Technically, silicones are not inherently bad. Linear cyclical silicones, like dimethicones or your MFA codes, are not dangerous to human health or the environment.
However, some brands stay away from them altogether because they don’t really have a health-forward standpoint point—in skin care, they make lotions feel nice and silky; in hair care, they provide a superficial coating around the strand and make it feel smooth and shiny. But they don’t provide nutrients or moisture, and they tend to stick on hair and skin.
“So it changes user behavior in a really interesting way,” notes Engler. “If you are using a hair cream that has a dimethicone in it, it doesn’t rinse out of the hair all that easy, and then you have to be super aggressive when you’re washing your hair.” Same goes for skin: “If you’re using a face cream that has one of these silicones, you’re going to have to be kind of aggressive to get it off, or it’s not all going to come off, and then it might clog pores,” Engler adds. We digress.
However! There is a class of nonlinear silicones, called cyclic silicones, that do actually build up in our waterways. Some examples are cyclotetrasiloxane (D4), cyclopentasiloxane (D5), cyclohexasiloxane (D6), and cyclomethicone. The more you wash and style with these silicones, the more they bioaccumulate in our water supply when they swirl down the drain. Read up on silicones here.