What Is It?
Dimethicone (also known as polydimethylsiloxane) – a silicon-based polymer – is a man-made synthetic molecule comprised of repeating units called monomers. Silicon is the second most abundant element in the Earth’s crust (after oxygen). Dimethicone is one of the most widely used ingredients in cosmetics and personal care products and can also be found in many cooking oils, processed foods, and fast food items.
According to 2019 data in U.S. FDA’s Voluntary Cosmetic Registration Program (VCRP), dimethicone was reported to be used in 12,934 products. This included products for use near the eye, shampoos and conditioners, hair dyes and colors, bath oils, skin care products, bath soaps and detergents, suntan preparations and baby products.
Why is it used in cosmetics and personal care products?
Dimethicone works as an anti-foaming agent, skin protectant, skin conditioning agent, and hair conditioning agent. It prevents water loss by forming a barrier on the skin. Like most silicone materials, dimethicone has a unique fluidity that makes it easily spreadable and, when applied to the skin, gives products a smooth and silky feel. It can also help fill in fine lines/wrinkles on the face, giving it a temporary “plump” look.
Scientific Facts:
Dimethicone is an important component in several toys, including Silly Putty, to which it imparts its unique viscosity and elastic properties, and Kinetic Sand, which mimics the physical properties of wet sand and can be molded and shaped into any desired form. Dimethicone is also a critical ingredient in rubbery silicone caulks, adhesives, and aquarium sealants, as well as water-repelling coatings, such as Rain-X.
Safety Information:
Dimethicone has undergone extensive review by scientific experts and authorities around the world.
U.S. CIR
In 2003, the U.S. Cosmetic Ingredient Review (CIR) Expert Panel reviewed the available literature and safety data for dimethicone as well as a group of closely related silicon polymers that function primarily as skin and hair conditioning agents and concluded dimethicone is safe as currently used.
U.S. FDA
The Food and Drug Administration (FDA) reviewed the safety of dimethicone and approved its use as a skin protectant in over-the-counter (OTC) drug products at concentrations from 1 – 30%. [21CFR347.10] Dimethicone is also an FDA approved food additive (antifoaming agent). [21CFR173.340]
European Union (EU)
Dimethicone is listed on the EU’s Inventory of Cosmetic Ingredients (CosIng) and its use as a cosmetic ingredient is not restricted in any way according to the General Provisions of the Cosmetics Regulation of the European Union.
World Health Organization (WHO)
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has established an acceptable daily oral intake level for dimethylpolysiloxane (dimethicone) of 0 to 1.5 mg/kg body weight. The maximum level (1.5 mg/kg body weight) is 100-fold lower than the level that caused no harmful effects in laboratory studies.
More safety Information:
CIR Safety Review: The CIR Expert Panel reviewed a group of silicon polymer
derivatives, including dimethicone, that are similar in structure, composition and use. The Expert Panel considered it unlikely that any of the silicone polymers would be significantly absorbed into the skin due to the large molecular weight of these polymers. Human clinical and laboratory absorption studies specific to dimethicone reported it was not absorbed following dermal exposure. Laboratory studies supported the safety of dimethicone following single or repeated oral, skin, or inhalation exposures. Laboratory and human clinical studies showed dimethicone was not irritating to the skin and did not cause allergic skin reactions (i.e., was not a skin sensitizer). It was also reported to be mild to minimally irritating to the eyes. In laboratory reproductive and developmental toxicity studies, no adverse findings were reported in dosed pregnant females or their offspring.
Dimethicone was also shown not to cause genetic mutations in multiple laboratory studies (i.e., not genotoxic). In several historical laboratory studies with mice where dimethicone was administered orally or on the skin for a lifetime, there was no evidence of increased tumor incidence (i.e., dimethicone was not carcinogenic).
Evaluating all available scientific data, CIR concluded dimethicone (and the other closely related silicon polymers) are safe as currently used in cosmetics and personal care products.
MYTH: Silicones, like dimethicone, will make your hair fall out.
FACTS: There is no scientific evidence to support this claim, which posits silicones in shampoos and conditioners build up on the hair and deprive the shaft of oxygen, resulting in hair loss. The Journal of Investigative Dermatology summarized this as follows: Silicone-based conditioners, such as dimethicone, are agents that aid in smoothing the hair cuticle and increasing hair smoothness and luster. Following water rinsing of a shampoo or conditioner, the silicone is left behind as a thin coating over each individual hair shaft to fill in visible defects in the hair cuticle, improving combing ease. Increased hair friction snags the hair as the comb is drawn for grooming purposes, resulting in hair breakage. This is the most common cause of significant hair loss in normal patients, patients with dandruff, and patients afflicted with female pattern hair loss. Compatibility of the hair can be increased by smoothing the cuticle and coating each individual hair shaft with an agent to decrease friction. Silicones fulfill this need.
MYTH: Some people are allergic to silicones like dimethicone.
FACTS: There is no scientific evidence to support this allegation. While a handful of people have made this claim in online forums, it is more likely they are allergic to another ingredient, such as a preservative. Unlike some preservatives that are known allergens, countless tests have been conducted with dimethicone and other silicones and have concluded these molecules are too large to physically enter the body past the upper layer of the skin to induce allergic reactions.
Resources:
Find out more about the regulation of over-the-counter drugs by the Food and Drug Administration