You may have seen it on the ingredient list of your shampoo, conditioner, cream, lotion, foundation, or makeup primer—dimethicone. What is this ingredient, and should you avoid it? What is Dimethicone? Dimethicone is what the chemists like to call a silicon-based polymer—”polymer” meaning it’s a large molecule made up of several smaller units bonded together. Simply put, it’s a silicon oil, man-made in the laboratory and used in personal care products as an anti-foaming agent, skin protectant, and skin and hair conditioner.