Polymethylsilsesquioxane: The Little Known Silicone



What Is Polymethylsilsesquioxane?

Polymethylsilsesquioxane is a type of silicone that is used in cosmetics and skincare products. It is used mainly as a protective ingredient but also helps to condition the skin and may help to improve the appearance of aging skin. 

Polymethylsilsesquioxane is a silicone. Silicones are synthetic polymers with a backbone composed 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 an element and the second most abundant element in the earth’s crust, after oxygen. In contrast, silicones are always synthetically produced.

What are the Best Skin Care Products of 2024?


the good:Help to improve the texture and feel of products, improving the spreadability and helps to give the skin a hydrated dewy appearance.

the not so good:Silicones are considered to be controversial ingredients despite being safe for cosmetic use. More on this below.

Who is it for?All skin types except those that have an identified allergy to it.

Synergetic ingredients:Works well with most ingredients

Keep an eye on:Nothing to keep an eye on here.

What Is Polymethylsilsesquioxane Used For?

As a class, silicones improve the feel, appearance, and performance of cosmetic products. These ingredients act as silky moisturizers, conditioners, solvents, and delivery agents for other skin care ingredients. Silicones are able to help with skin redness and irritation due to their low surface tension, which enables them to spread easily across the surface of the skin and form a protective covering.

Protective barrier 
Polymethylsilsesquioxane functions as a film-forming agent by forming an invisible film on the surface of the skin. The film creates a lubricating, smooth, silky feel that does not feel greasy or sticky. It still allows oxygen, nitrogen, and other important nutrients to pass through but blocks water from evaporating. Ultimately, this leads to skin that looks and feels hydrated and smooth. Additionally, the film formed by polymethylsilsesquioxane has excellent water-repellency. This property is useful for the formulation of sun protection products.

Polymethylsilsesquioxane is also frequently used in anti-aging skin care products. As mentioned above, this ingredient helps the skin to retain moisture better. This is important because one of the major factors that contribute to aging skin is loss of moisture. By keeping the skin moisturized, fine lines and wrinkles are less likely to form. Another reason to use polymethylsilsesquioxane in anti-aging products is due to its ability to temporarily fill in fine lines and wrinkles, giving the skin a more plump appearance.

What Are Silicones?

Silicones are a skincare ingredient used to improve the texture and the appearance of your skin. There are a few things that are useful to know about silicones when investigating why they’re in your skincare products. Silicones are organosiloxanes, which means that they are a molecule that has alternating silicone and oxygen atoms along a carbon chain or ring—silicones where originally sourced from sand in the form of silicon dioxide. 

There are three main categories of silicones that are used in cosmetic and skincare products. The first is small silicones, the second is silicone polymers or long-chain silicone molecules, and functional silicones which are characterized by their shape and structure. Most silicones can be identified by the end of their name. If an ingredient ends in -cone, -siloxane or -conol, then it is probably a silicone. 

What Are The Concerns Around Polymethylsilsesquioxane?

Despite polymethylsilsesquioxane and other silicones being considered to be both safe and effective for cosmetic purposes, a multitude of rumors exist claiming they are unsafe for topical use.

 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 supported in any published research.

To dispel these claims, it’s first important to understand that the large molecular size of silicones prevents them from being absorbed by the skin. If a substance cannot penetrate the skin, it is unlikely to cause toxicity or immunity issues. This is why silicones are not considered to be allergens.

 Additionally, claims that silicones can bioaccumulate or build-up in our bodies is also not supported. Once again, this is because their large size prevents them from penetrating the skin. If silicones cannot penetrate the skin, they certainly cannot pass through cell membranes, a key requirement for bioaccumulation.

Lastly, it is incorrect to say that the film formed by silicones suffocates the skin. As mentioned above, the soft, invisible film that polymethylsilsesquioxane and other silicones form after topical application allows oxygen and other gases to pass through. Furthermore, the film does not block natural oil secretion. Thus, the skin can still ‘breathe’ after topical application of a product containing silicones.

Is Polymethylsilsesquioxane Safe?

The safety of polymethylsilsesquioxane and its derivatives has been assessed by the Cosmetic Ingredient Review Expert Panel, a group responsible for evaluating the safety of skincare and cosmetic ingredients. The Expert Panel evaluated the scientific data and concluded that polymethylsilsesquioxane and its derivatives are safe for use in cosmetics and personal care products.

References:Yahagi, K, 1992. ‘Silicones as conditioning agents in shampoos’, Journal of the Society of Cosmetic Chemists, vol. 43, pp. 275-284. 

Mojsiewicz-Pieńkowska, K et al., 2016. ‘Direct human contact with siloxanes (silicones)- safety or risk: Part 1 Characteristics of siloxanes (silicones), Frontiers in Pharmacology, vol. 7, pp. 132. 



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