Cyclic siloxanes D4, D5 and D6 are chosen for their low toxicity, lack of skin smoothness and ease of formulation. They bring benefits to personal care products like silkiness in conditioners, volume in lip gloss and ease of application to deodorants. Industry has carried out a body of research on the health impacts of these substances.
A recent study (M.B. Reddy et al., Modeling of Human Dermal Absorption of Octamethylcyclotetrasiloxane (D4) and Decamethylcyclopentasiloxane (D5), Toxicological Sciences 99(2), 422-431 (2007)) has shown that when applied to the skin of human volunteers, between 0.12-0.3% of D4 and 0.05% of D5 are absorbed. More than 83% of the substance that reaches systemic circulation was eliminated within 24 hours. Exhalation is the main mode of clearance of the small amount that penetrates through the skin.
The silicone industry also cooperated with the Scientific Committee for Consumer Products (SCCP), a European Commission expert group by providing an extensive dossier on D4 covering all of the relevant toxicological endpoints. The SCCP published an Opinion on D4 in December 2005 (the Opinion can be downloaded from here).
In its conclusions, the SCCP stated:
"The following information is required before any further consideration:
This information should be supplied by 1 October 2006."
CES provided the information requested to the SCCP secretariat within the required timeframe. The Scientific Committee for Consumer Products (SCCP) has published its final opinion on 22 June 2010 which states that: “The SCCS is of the opinion that cyclomethicone (D4, D5) does not pose a risk for human health when used in cosmetic products."
Industry's assessment of the findings is that the use of D4 is safe in the intended personal care applications by a wide margin.
An extensive body of toxicological information is available on D5.
Since then, the silicone industry has undertaken more research addressing questions raised about the relevance to humans of toxicological data obtained from long-term rat studies (Note: the silicone industry position about animal studies is that in the current state of the legislation they are required by governmental agencies to demonstrate the safety of chemicals. The silicone industry is committed to reduce the number of animals to the minimum required; in addition, it supports the development and implementation of alternative methods provided they are reliable and validated).
Further information on the health safety of D5 can be found on the silicone industry's US website managed by SEHSC, CES' sister organisation in North America.
CES and its members firmly believe that D5 and D6 are also safe when used as intended and continue to work to show this.
In North America, Health Canada has also reviewed the health properties of the cyclosiloxanes D4 and D5. They concluded that “based on the available information on its potential to cause harm to human health, it is concluded that D4 [and] D5 [are] not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.”