Cyclopentasiloxane (D5)

What Is It?

Cyclomethicone is a general term describing an individual and/or a mixture of cyclic siloxane materials that have many uses and are found in a variety of consumer products. These materials are derived from the natural elements silicon and oxygen.

The basic structure common to all cyclomethicones is a cyclic backbone of siloxane units (i.e., silicon and oxygen with molecules of carbon and hydrogen attached, all very common elements found in nature).  Shorthand nomenclature is based upon the number of siloxane groups in the cyclic structure (Figure 1).  Thus, cyclomethicone D5 (also known as cyclopentasiloxane or just D5) has five of these groups.

Figure 1.  A molecule of cyclopentasiloxane (D5)

Why is it used in cosmetics and personal care products?

Cyclopentasiloxane (D5) is the predominant cyclomethicone used in cosmetics and personal care products, primarily due to its excellent skin conditioning and hair conditioning properties. It is also used as a solvent. D5 and similar cyclomethicone ingredients are used in products where eventual complete evaporation of the siloxane carrier fluid is desired, such as deodorants and antiperspirants that need to coat the skin but not remain tacky afterward. Other important product performance benefits include facilitating a smooth texture and an even application. Thus, they may also be found in sunscreens, shampoos, conditioners, moisturizers, lotions, etc.

Scientific Facts:

Cyclomethicones create many of the positive qualities we associate with personal care products: luxuriant texture, silky smoothness, luster and smooth application. They help make personal care products non-stinging and non-irritating. For example, silicones reduce the white residue and tacky feel of antiperspirants and help “long-lasting” makeup retain its color and luster. With cyclomethicones, shampoos and conditioners have better shine; wetting and spreading qualities provide for smooth and even application of makeup, lotions, sunscreens and cleansers.

More Information on Other Cyclomethicones

Safety Information:

United States (U.S.)
The safety of the cyclomethicones (including D5) has been reviewed on several occasions by the Cosmetic Ingredient Review Expert Panel (CIR). In 1991, the Panel reviewed available safety information for cyclomethicone (defined as a mixture of cyclomethicone compounds with 3-7 siloxane groups (i.e., D3-D7)) and concluded it was safe in the present practices of use. In 2009, the Panel re-opened the report on cyclomethicones in order to consider new data and to include the individual chain length compounds, now identified as separate cosmetic ingredients, including cyclopentasiloxane (D5). Considering all of the additional data, the Panel again concluded that D5 and the other cyclomethicone ingredients reviewed (cyclomethicone mixture and D4-D7) were safe under current practices of use.

European Union (EU)
The EU’s Scientific Committee on Consumer Safety (SCCS) reviewed the safety of cyclopentasiloxane (D5) in 2010 and concluded that it does not pose a risk for human health when used in cosmetics and personal care products. SCCS also noted, however, that D4 (a potential residual starting material in the manufacture of D5) is classified in Europe as toxic to reproduction. For this reason, cosmetics and personal care product manufacturers closely monitored and controlled the residual levels of D4 in the cyclomethicones used in their products (i.e., D5 and D6). In a second review of cyclopentasiloxane (D5) safety in 2015, the SCCS also noted that it might contain traces of cyclotetrasiloxane (D4) and that the level of D4 as an impurity should be as low as possible. The SCCS recommended that the level of purity of D5 in cosmetics put on the market should be > 99%.

In 2018, the European Chemicals Agency’s (ECHA) Member State Committee concluded that D5 met the criteria for a very persistent, very bioaccumlative (vPvB) substance in the environment. Based on those findings, the European Commission amended Annex XV to REACH indicating that D5 should not be placed on the market in wash-off cosmetics products in a concentration at or above 0.1% after January 31, 2020. The concentration limit set by this restriction effectively ensured that all intentional use of D5 in the EU ceased, since the substance must be present in wash-off cosmetic products in a much higher concentration to perform its intended function.

In 2019, the restriction’s scope was expanded to include leave-on cosmetics products. While ECHA maintained its conclusions, the restriction for leave-on products has not entered into regulation as of April 2021.

In 2006, the Canadian government announced its comprehensive strategy for managing chemicals (Chemicals Management Plan) as a way to gather information on approximately 4,000 of the 23,000 materials in commerce in Canada. These substances were categorized for further assessment to determine potential risks to health or the environment. Inclusion in the program did not indicate a potential risk but allowed the Canadian government to gather information that would help provide a more complete understanding of the human health and environmental effects of each material. Several siloxane (cyclomethicone) materials, including D4, D5 and D6 were included in this program. An analysis of all safety studies and data on exposure through use in cosmetics products showed that none of these substances present a risk to human health as currently used. After reviewing information on bioaccumulation of these siloxanes, the Government of Canada concluded that siloxane D5 is not harmful to human health or the environment.

More safety Information:

The Silicones Environmental, Health, and Safety Center (SEHSC) of the American Chemistry Council, which is committed to the responsible use of silicones, continues to evaluate the science behind silicone and siloxane materials through rigorous research programs. Research methodologies include computer modeling, laboratory testing, environmental monitoring and other approaches.