Photo: Robert Trachtenberg

Not long ago I was chatting in my office with Scottsdale, Arizona, dermatologist Jennifer Linder, MD—one of the loveliest nerds I know—about something of great interest to her: silicones. (This is how she talks: "Silicones, or polysiloxanes, are characterized by a silicone-oxygen backbone. Side groups attached to the silicones vary....") When I mentioned that I'd never liked the idea of putting silicone on my face because I thought it was pore clogging, she gracefully pointed out that silicone doesn't penetrate the skin, so it can't clog pores. Then she said it's inert (meaning that it doesn't react with the skin), so it doesn't cause breakouts. What it does do: create a silky film that reduces moisture loss (good for the skin)—and helps makeup go on smoothly, which is why it's often one of the main ingredients in foundation primers. So when you see dimethicone or cyclomethicone in an ingredient list, you can think, Complexion-friendly. Who knew? Thanks, doctor!

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