The safety of the cyclomethicones has been reviewed on several occasions by the Expert Panel for Cosmetic Ingredient Safety.  In 1991, the Expert 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 that it was safe in the present practices of use.  In 2009, the Expert Panel re-opened the report of cyclomethicones in order to consider new data and to include the individual chain length compounds now identified as separate cosmetic ingredients.  Their review included D4, D5, D6 and D7.  Considering all of the additional data, the Expert Panel again concluded that these cyclomethicone ingredients were safe under current practices of use.

The EU’s Scientific Committee on Consumer Safety (SCCS) reviewed the safety of D4 and D5 in 2010 and concluded that cyclomethicones (D4 and D5) do not pose a risk for human health when used in cosmetic products.  SCCS also noted, however, that D4 was being classified in Europe as toxic to reproduction.  This is the reason that cosmetic and personal care product manufacturers closely monitor and control the residual levels of D4 in the other cyclomethicones that are used in their products (i.e., D5 and D6).  In fact, in a second review of cyclopentasiloxane (D5) safety in 2015, the SCCS noted that it might contain traces of cyclotetrasiloxane (D4). Therefore, the level of D4 as an impurity of D5 should be as low as possible. The SCCS recommended that the level of purity of D5 in cosmetic products put on the market should be > 99%.

Subsequent to these EU human safety reviews, the United Kingdom submitted a dossier to the European Chemicals Agency (ECHA), proposing a restriction for personal care products that are washed off in normal use if they contain more than or equal to 0.1% by weight of cyclotetrasiloxane (D4) and cyclopentasiloxane (D5).  The restriction was based on the ECHA conclusions regarding environmental properties of D4 and D5 (bioaccumlation and persistence).  A public consultation on the proposed restriction ended in December 2015.  The restriction, if approved, is proposed to enter into force at least two years after the date of its publication in the Official Journal of the European Union.

In 2006, the Canadian government announced its comprehensive strategy for managing chemicals, the Chemicals Management Plan, as a way to gather information on approximately 4,000 of the 23,000 or so 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 cosmetic 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 and D6 are not harmful to human health. However, they concluded that only siloxane D4 may cause harm to the environment or its biological diversity. The Government of Canada is developing measures to control the potential risks posed by siloxane D4. Environment Canada will review and consider the development of additional risk management controls for siloxane D4, if required, as more information becomes available.

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.