Phthalate & Silicone alternatives: Preservative deep dive

DEP is also used as a denaturing agent and it can be found in SDA Alcohol 39 C endorsed by the US Government. Although DEP remains a theoretical possibility for the denaturation of alcohol in the EU, other systems are preferred.

As recommended by the EU Commission, either Isopropyl Alcohol (IPA) and/or tert-Butyl Alcohol (TBA) should be added to alcohol as a minimum denaturant in the manufacture of certain products in cosmetic and perfume production. These denaturants should be used in products with an alcohol level above 20%, or 5% for mouthwash.

Silicones

Unlike the Parabens or the Phthalates, the Silicones are a vast family of chemicals only related by a common structural pattern made of silicon and oxygen. As a consequence, Silicones can have all kinds of properties and be used for all kinds of purposes.

There are entire books focusing on the cosmetic applications of Silicones6 and this article does not intend to provide an exhaustive list of the commercially available silicones and their alternatives. The focus will be on two particularly infamous silicones, regularly criticized by cosmetic products reviewers: Dimethicone (CAS 63148-62-9 / 9006-65-9 / 9016-00-6) and Cyclopentasiloxane (so-called D5, CAS 541-02-6).

Dimethicone is a simple polymer of the structure outlined above, with R = Methyl. Its use started in the fifties, the first Silicone formulated in personal care products. Today, this is the most common and the least expensive Silicone available on the market.

Amongst its numerous qualities, Dimethicone is colorless, inert and exists in a great range of viscosity, which allows its use in skincare, hair care and color cosmetics. Typically, Dimethicones with low to medium viscosity (5 to 1,000 cst) are widely used in skincare products while high-viscosity Dimethicones (60,000 to 100,000 cst) are more commonly used in hair care products.

In skincare products, Dimethicone is particularly appreciated for its ability to fill in uneven texture and fine lines. It helps create a smooth look in products like foundations. As a consequence of its hydrophobicity, it also provides a protective cover on skin, which helps retain moisture. In hair care products, Dimethicone is used to smooth hair, provide better comb-through and add some sheen.

So, what is wrong with Dimethicone?

Dimethicone is a safe ingredient that can be used without any legal restriction in the EU. The main problem of Dimethicone is its very low solubility in water and its resulting coating action: it is accused of building up on hair and making it heavy, flat and greasy. Removing Dimethicone from the hair would then require aggressive sulfate-based shampoos, which are known to dehydrate and weaken the hair.

In skincare products, Dimethicone has been reported to create an artificial coating that traps everything under it, causing breakouts and blackheads. Furthermore, it would prevent the other cosmetics applied from accessing the skin. On top of that, and this claim is at least partly true, Dimethicone does not biodegrade easily and represents a threat for the environment.

Cyclopentasiloxane (D5) is a Dimethicone chain of five units, with units 1 and 5 linked together to form a cycle. The greatest advantage of D5 is to impart a dry and pleasant skin feel, which consumers appreciate. It is a fast-spreading emollient that helps spread the emulsion homogeneously on the skin to evenly distribute active ingredients.

Unfortunately D5 raised both safety7 and environmental concerns8 in the EU9 (as well as other countries such as Canada). The initial restriction of D5 at less than 0.1% in wash-off products should be extended to leave-on products, causing the end of this remarkable ingredient at relatively short notice10.

Two big options exist when it comes to replacing Dimethicone and Cyclopentasiloxane, namely with or without Silicones.

Silicone alternatives

Some Silicone derivatives have good to excellent solubility in water and, therefore, do not show the same disadvantages as Dimethicone. However, they have similar qualities, with especially excellent hair conditioning properties and the ability to impart a silky soft feel to the skin.

This is notably the case for Dimethicone Copolyols, which are classified by their ratio of ethylene oxide and propylene oxide molecules. For instance, Bis-PEG/PPG-14/14 Dimethicone is Dimethicone end-blocked with an average of 14 moles of ethylene oxide and 14 moles of propylene oxide. The biggest drawback of these water-soluble Silicones is probably their price.

Regarding D5, the unique dry skin feel characteristic of this ingredient is not due to its volatility, which is very low at skin temperatures, but to its low surface tension. This effect can be mimicked by mixing small amounts of alkyl Silicones with natural oils (e.g. behenyl dimethicone is soluble in soybean oil and reaches a critical micelle concentration at about 4%, at which point it gels the oil).11

Silicone-free alternatives

Many Silicone-free options are available on the market although it is rather difficult to find a one-to-one replacement. Dimethicone may be replaced by mixtures such as:

• Coco-Caprylate/Caprate (e.g. Cetiol LC, BASF), considered as a medium spreading emollient “for modern cosmetic applications”
• Butylene glycol Dicaprylate/Dicaprate (e.g. Dermofeel BGC, Evonik Dr. Straetmans GmbH)

Another category of substances reported to have very similar properties to Silicones are the Alkanes. For instance, Coconut Alkanes seem to offer an acceptable alternative to some forms of Dimethicone (e.g. the interesting mixture Coconut Alkanes and Coco-Caprylate/Caprate, Vegelight 1214 LC, Biosynthis). Of course, this approach is not compatible with the use of the marketing claim “free from mineral oils”.