Dimethicone, also known as dimethylpolysiloxane or Polydimethylsiloxane (PDMS), is a linear organosilicon polymer widely used in a highly varied range of personal care formulations. It is a medium-viscosity clear liquid. Dimethylpolysiloxane is the most popular silicon-based non-reactive organic polymer in the skincare industry and medicine, thanks to its beneficial properties (low surface tension and a high spreading coefficient).
Simethicone also called activated dimethicone, is a mixture of PDMS and silicon dioxide used in pediatric practice as an antifoaming agent and carminative to decrease gas bubble formation in newborns' gut and soothe discomfort. It is also the principal component of silicone breast implants.
Dimethicone is usually used in oil-free facial creams, masks, moisturizers, as well as sunscreens, and antiperspirant/deodorant compositions. It decreases transdermal water loss without a greasy feel. In addition, its high permeability to water vapor and oxygen doesn't seal the skin and allows respiration (skin "breathing").
In skin care formulations, it imparts a hydrophobic, protective, but breathable barrier to the skin and improves spreading characteristics while reducing whitening and foaming effects during rub-in and imparting lubricity and softness. PDMS is also used in hair care formulations as a conditioning agent that also enhances shine and reduces stickiness.
It has occlusive and emollient properties and is suitable for acne and sensitive skin as it is non-comedogenic and hypoallergenic. CIR Expert Panel threat dimethicone as "safe as used in cosmetic formulations."