Peg-10 dimethicone is a type of silicone that is used in hair and skin care products as a conditioning agent, lubricant, and skin protectant.
PEG-10 dimethicone is a type of silicone. Silicones are synthetic polymers made up of repeating units of siloxane (elemental silicon and oxygen), which is why silicones may also be referred to as polysiloxanes. Often, the terms “silicone” and “silicon” are mistakenly used interchangeably, when they are actually quite different. Silicon is the 14th element on the periodic table and the second most abundant element in the earth’s crust, after oxygen. In contrast, silicones are always synthetically produced.
Dimethicone, also known as polydimethylsiloxane, is comprised of organic (carbon-based) groups attached to a linear inorganic backbone of silicon and oxygen. The prefix ‘‘dimeth” refers to the two methyl groups that are attached to the silicone molecule to form dimethicone. Based on this structure, dimethicone is considered to be a hydrophobic (lipid soluble) oil. One way to make dimethicone more water-soluble is by adding multiple units of ethylene glycol to sites along the polymer chain. The oxygen atoms add polarity to the silicone and are readily available for association with water molecules. This process is called ethoxylation or polyethylene glycol (PEG)-modification.
Prior to 1999, all silicone compounds that contained PEG groups were classified as dimethicone copolyols. This term encompassed any amount of polyethylene glycol (PEG). However, in 1999, the INCI rules were changed and required manufacturers to disclose the number of moles of ethylene glycol present in a dimethicone copolyol. Thus, the number associated with the ingredient name (i.e., PEG-10 dimethicone) corresponds to the number of repeat units of ethylene glycol. The greater the number following the PEG designation, the “heavier” and more complex the molecule.
As a class, silicones improve the feel, appearance, and performance of products. They act as silky moisturizers, conditioners, solvents, and delivery agents for other ingredients, as well as improve product spreadability. Upon application to the skin, silicones form a film on the surface while still allowing skin to “breathe”. Oxygen, nitrogen, and other nutrients can still pass through the film formed by silicones. However, most silicones do not allow water to pass through, which is an ideal quality for preventing dry, dehydrated skin. Silicones provide an exceptionally desirable skin-feel that is dry and non-greasy, yet silky smooth.
More specifically, PEG-10 dimethicone functions to condition, lubricate, and protect the skin. The combination of silicone with methyl groups tends to make it extremely resistant to water, yet it keeps them flexible and moving free, ideal properties for a lubricant. Due to its large molecular size, PEG-10 dimethicone is poorly absorbed into the skin. Therefore, upon application, PEG-10 dimethicone not only prevents water loss, but also protects the skin from penetration of harmful substances, such as irritants and bacteria. Thus, PEG-10 dimethicone can be classified as a skin protectant.
PEG-10 dimethicone is also commonly used in hair care products. The hydrophobic portion of PEG-10 dimethicone works to make hair shiny and slippery, as well as prevents tangles. Furthermore, the water-soluble portion of this ingredient prevents product build-up, which is a common problem for other non-water soluble silicones.
The Cosmetic Ingredient Review (CIR) Expert Panel reviewed the safety of 62 dimethicone crosspolymer ingredients, including PEG-10 dimethicone. The Panel concluded that these dimethicone crosspolymer ingredients are safe as used in cosmetics and personal care products.
Despite the approval by the CIR Expert Panel, PEG-10 dimethicone is often called a “toxic” ingredient that should be avoided. One reason PEG-10 dimethicone has received a bad reputation is due to possibly contamination with 1,4-dioxane. As mentioned above, the process of making PEG-10 dimethicone involves ethoxylation, which produces 1,4-dioxane as a byproduct. According to the National Toxicology Program, “1,4-dioxane is reasonably anticipated to be a human carcinogen.”
Additionally, there are claims that silicones as a class can cause or worsen skin concerns, cause sensitization, and “suffocate” skin. However, these claims have not been proven in any published research. The large molecular size of silicones, including PEG-10 dimethicone, prevents them from being absorbed by the skin. If a substance cannot penetrate the skin, it cannot react with cells of the immune system. Thus, silicones (including PEG-10 dimethicone) are not allergens. In fact, according to Skin Inc., silicones are so biologically inert when in contact with the skin, silicones are now replacing latex, a common allergen in adhesives, gloves, and a wide array of other items.
References: Cosmetics and Toiletries, “Bis-PEG vs. PEG dimethicone”, 2008, Naturally Curly, “Water Soluble Silicones 101”, 2012, Vet Med Int. 2013; 2013: 239186, Cosmetic Ingredient Review, “Safety Assessment of Dimethicone Crosspolymers as Used in Cosmetics”, 2012.