What it is
Dimethicone crosspolymer is a high-molecular-weight silicone elastomer made of dimethicone polymer chains that have been chemically crosslinked into a soft, rubber-like, three-dimensional network. In a finished product it is typically swollen in and blended with a base silicone fluid such as dimethicone or cyclopentasiloxane, forming a gel that thickens the formula and controls its flow. On skin it spreads into a thin film that imparts a silky, smooth, dry feel and helps blur the look of pores and fine lines, which is why it is common in primers, foundations, and sunscreens. Because it is a large polymer rather than a small molecule, it works at the surface as a sensory and texture modifier rather than penetrating the skin.
Safety & warnings
Dimethicone crosspolymers are generally well tolerated. The Cosmetic Ingredient Review Expert Panel concluded that these ingredients are safe in the present practices of use and concentration, noting that as large polymers they will not penetrate the skin and that the silicone backbone is stable under anticipated conditions of use. In testing, dimethicone crosspolymer was not dermally irritating in animal studies and was not irritating in human irritation tests, and the Panel addressed and was reassured about residual monomer content. Silicones like this are non-comedogenic for most users, though people who prefer to avoid silicones for personal or texture reasons may choose to skip it.
Origin & sourcing
It is a synthetic silicone material, not naturally occurring. According to the Cosmetic Ingredient Review, the majority of dimethicone crosspolymers are produced by crosslinking dimethicone polymer chains through a hydrosilation reaction, in which silicon-hydride (Si-H) bonds add across vinyl bonds on a bifunctional crosslinking agent. These reactions are typically driven by a platinum catalyst, proceed rapidly, and yield chemically stable products.
History
Crosslinked silicone elastomers were developed by the personal-care and silicone industries as a way to give silicone-based formulas body and an elegant, powdery slip. The Cosmetic Ingredient Review published a consolidated safety assessment covering dimethicone crosspolymers as a group, reviewing the animal and human data and the question of residual monomers for these polymers.
Questions everyone asks
What does dimethicone crosspolymer do in a sunscreen?
It thickens and stabilizes the formula and gives a smooth, silky, fast-spreading feel, helping the product glide on and sit evenly without a heavy or greasy finish.
Is dimethicone crosspolymer the same as dimethicone?
They are related but not identical. Dimethicone is a fluid silicone, while dimethicone crosspolymer is that silicone chemically crosslinked into a soft, gel-like elastomer used mainly to modify texture and thickness.
Is dimethicone crosspolymer safe for the skin?
The Cosmetic Ingredient Review Expert Panel concluded it is safe as used in cosmetics, noting it is a large polymer that does not penetrate the skin and was not irritating in testing.
Will it clog pores?
Silicone elastomers like this are widely considered non-comedogenic and sit on the skin surface, though individual results vary, so anyone prone to congestion can patch test.