Decamethylcyclopentasiloxane, commonly known as D5, is a volatile cyclic siloxane frequently used in skincare products, sunscreens, foundations, hair care products, and cleansers. It enhances the smoothness and spreadability of formulations while providing a dry, lightweight skin feel—a property that once made it a key ingredient for achieving a desirable sensory experience in many products.
The EU’s decision to restrict D5 is not primarily due to acute dermal toxicity, but rather because the substance is "too stable" in the environment. D4, D5, and D6 are classified as substances that are highly persistent and highly bioaccumulative; D4 is further categorized as persistent, bioaccumulative, and toxic (PBT). Furthermore, if D5 contains D4 as an impurity above certain levels, it may also pose a PBT risk. Because these substances do not readily degrade and can accumulate in water, soil, and living organisms, the EU has imposed concentration limits on their use under the REACH regulation.
According to EU Regulation (EU) 2024/1328, restrictions on D4 and D5 in "rinse-off" cosmetic products have been in effect since 2020, with restrictions on D6 in such products set to apply from June 6, 2026. For "leave-on" cosmetic products, restrictions on D4, D5, and D6 will take effect after June 6, 2027, generally setting a maximum concentration limit of 0.1% by weight. It should be clarified that D5 is not simply labeled as a "toxic ingredient"; rather, it is subject to stricter regulation due to its environmental risks. For companies engaged in foreign trade and regulatory compliance, the focus should be on ensuring raw material purity, controlling residual cyclic siloxane content, and verifying the specific concentration limits applicable to their target markets.