Simply put, dimethicone is silicon oil and is similar to the caulking used to make your shower water proof. Dimethicone is manufactured in a laboratory for use in personal care products as a skin protectant and an anti-foaming agent. Instead of sinking into your skin and nourishing it, like healthy ingredients do, dimethicone forms a plastic-like barrier on the outside of your skin. 

Dimethicone is silicon-based polymer that is suspected to be an environmental toxin because it is not biodegradable. There are also concerns over its organ system toxicity potential. You will find this ingredient hiding in your lotions, hair conditioners and water proof sunscreens.