The Truth About Dimethicone

At Naturium we are committed to creating biocompatible formulas which means delivering bioactives to the site of action with minimal disruption to the skin and in harmony with the skin. We carefully select ingredients that enhance bioavailability or efficacy while being non-irritating. Once such an ingredient is dimethicone.

Dimethicone falls into the broad category of silicones. Silicones are inorganic polymers formed from quartz also called silica or silicon dioxide. Although silicones originate from a natural source the chemical processing to become silicones makes them synthetic. Silicones are a very unique category of ingredients that are neither water soluble or oil soluble. Silicones have a backbone of silicon atoms attached to oxygen atoms [-O-Si-O-Si-O-]. These silicon oxygen bonds are long bonds with a very low barrier to rotation (twist easily) and wide bond angles leading to low intermolecular forces between atoms^a. This makes silicones very flexible with continually changing orientation which give silicones its unique sensory properties that consumers perceive as slippery, non-tacky, smooth, and silky.

Not all silicones are created equal. The silicone length or degree of polymerization, chemical groups attached to the silicon atoms, and degree of branching strongly dictate the function and characteristics of the silicone. Dimethicone is a fully methylated linear siloxane polymer terminated by trimethylsiloxy units. The “di” means two and “meth” refers to the methyl or CH3 groups. There are two methyl groups attached to every silicon atom except for the two ends which have three methyl groups. Dimethicone is an inert, non-volatile silicone. Its use is not restricted due to environmental bioaccumulation like cyclomethicones.^b Due to the long bond lengths resulting in large spacing between atoms, dimethicone has a high gas permeability. This makes for a porous membrane or breathable film when applied to the skin so it won’t clog pores or prevent bioactives from penetrating the skin. The Cosmetic Ingredient Review (CIR) Expert Panel has deemed dimethicone as safe and non toxic in cosmetic products.^c Studies show that it does not absorb into the skin or penetrate the skin barrier so there is no perceived risk of systemic toxicity. Due to its large molecular weight, dimethicone sits on the surface of the skin. It very rarely causes irritation and can be used as an OTC skin protectant making it safe for even the most sensitive skin.^d

So why use dimethicone in skin products? Dimethicone helps with the spreadability of the formulas which is important for a uniform application. A uniform application is vital for bioavailability or efficacy of a product. Silicones offer better spreadability than oils and esters due to their low surface tension. You may have noticed that some lotions or creams look white on the skin when you try to rub it in. This phenomenon is called soaping. That means the surface tension of your cream is greater than the critical surface tension of the skin and resists spreading. The skin has an average surface tension of 28 dynes/cm² while silicones have an average surface tension of 19.9+/- 0.9 dynes/cm², vegetable oils 32.8 +/0.5 dynes/cm², and esters 29.1+/- 2.1 dynes/cm².^e Using silicone replacements, vegetable oils, or esters won’t lower the surface tension of your cream as well as silicones. Dimethicone improves spreadability in formulas enhancing efficacy, performance, and sensorial attributes.