* A silicone

* Also known as Dimethicone

* Please read TIA's article on What Is It: Silicones and Should We Avoid Them

Functions:

Polydimethylsiloxane is a widely-used and versatile ingredient seen in many skin care and beauty products because of its ability to serve as an anti-foaming agent, skin protectant and conditioner; it is known to prevent water and moisture loss in the skin by forming a hydrating barrier. According to research published in Skin Research and Technology, this barrier also serves as a mild water repellent, and has been shown to fill in fine lines, giving skin a temporary “plump” look. Polydimethylsiloxane is an easily spreadable silicone oil that creates a coating when applied to the skin that feels smooth and silky to the touch, although this effect is superficial.

According to a study performed on barrier cream at King's College London, the protective barrier formed on the skin by Polydimethylsiloxane can protect skin from external infections, reduce redness caused by rosacea, has anti-inflammatory properties, can soothe and protect the skin of patients suffering from Sodium Lauryl Sulfate-induced irritant contact dermatitis, and possibly prevent the formation of contact dermatitis, especially on the hands. As a non-comedogenic ingredient, it can protect the skin without adding heaviness or clogging pores. Polydimethylsiloxane has also been shown to enhance the light refractability of other ingredients, and is therefore an ingredient included in many sunscreens and cosmetics. It is also seen in many facial moisturizers, body lotions, sunscreens, anti-aging serums, eye creams, foundations, facial powders, eye shadows, hair conditioners and hair dyes.

According to Wikipedia, Polydimethylsiloxane "has also been used as a filler fluid in breast implants, although this practice has decreased somewhat, due to safety concerns, despite some evidence that it may be protective against breast cancer. It continues to be used in knuckle replacement implants, with good results." It is also a 4% component in Silly Putty thanks to its viscoelastic properties, and a popular ingredient in contact lens solutions.

Safety Measures/Side Effects:

Polydimethylsiloxane is considered to be a 100% safe ingredient by the Cosmetics Database and the FDA approves it as a safe food additive.

Although a large amount of research has connected silicones to cancer and organ failure, it is generally considered to be a hazardous ingredient when injected into the skin or body, but not when applied topically. Many studies find silicones, including Polydimethylsiloxane, to be safe when used in the body as well, including a study published in the New England Journal of Medicine, in which after a 14 year study of over 1,000 women with breast implants, a team of researchers and doctors concluded that "we did not find an association between silicone breast implants and connective-tissue diseases, defined according to a variety of standardized criteria, or signs and symptoms of these diseases."

According to TIA's post on silicones, it's been determined that silicones do not cause allergic reactions, although they do remain on or near the skin's surface. Silicone molecules, like those found in polydimethylsiloxane, are too large to penetrate the skin and the cell membranes. However, they can increase the ability for other ingredients with smaller molecules to penetrate the skin, and can make it susceptible to toxins.