The U.S. Environmental Protection Agency (EPA) recently released a draft risk assessment for cyclotetrasiloxane (D4, CAS No. 556-67-2) under the Toxic Substances Control Act (TSCA) and simultaneously launched a public comment period. This news, confirmed by the U.S. Technical Barrier to Trade Addendum Notification to the World Trade Organization (WTO), marks a new phase in the coordinated global regulation of D4.

The assessment focuses on the entire life cycle and preliminarily determines dual risks.

Initiated by the EPA at the manufacturer's request, the assessment focuses on D4's "Conditions of Use" (COUs)—covering the entire life cycle of production, processing, transportation, use, and disposal, including specific application details such as industrial operating procedures and the percentage of additives in consumer products. Based on the weight of available scientific evidence, the EPA preliminarily concludes that D4 may pose an "unreasonable risk" to human health and the environment.

This assessment echoes the findings of international research. A long-term toxicity study previously published in PubMed showed that exposure to high concentrations of D4 can cause damage to the female reproductive system and liver and kidney abnormalities. The European Union has already classified it as a substance of very high concern (SVHC) that "may impair fertility" and "extremely toxic to aquatic organisms." Notably, the EPA emphasized in its assessment that it will no longer assume the regulated use of personal protective equipment (PPE) in occupational settings, and will more rigorously consider actual exposure risks.

The public can provide 10 key areas of feedback to enhance transparency in the regulatory process.

The draft assessment has been made public through the US government's official website (https://www.regulations.gov), and the public can submit feedback on 10 key areas, including the application of pharmacokinetic models, accuracy of hazard identification, effectiveness of exposure control measures, and completeness of bioaccumulation data. The EPA stated that public feedback will serve as an important basis for refining the assessment's conclusions, and that peer review will be conducted to ensure scientific integrity. Global regulatory efforts are merging, putting pressure on the beauty and other industries to transform.
This US action is not an isolated incident, but rather a reflection of tightening global D4 regulations.
The EU passed an amendment to the REACH regulation in 2024, explicitly banning D4 in concentrations of 0.1% or higher in cosmetics and other products starting in 2026, with the ban extended to nearly all consumer goods in 2027.
The draft cosmetics standards recently released by the China National Institute for Inspection and Quarantine also propose adding D4 to the list of banned ingredients.
The EU had already taken the lead in banning D4 in its Cosmetics Regulation, and Chinese brands like Huaxikou added it to the banned list as early as 2019, three years ahead of the EU ban.
"D4's persistence, bioaccumulation, and potential toxicity are the core reasons for the tightening global regulation." Industry analysts point out that the substance can be transported long distances through the air, has been detected in remote areas such as the Arctic, and is difficult to degrade naturally. Currently, industries like chemicals and cosmetics have begun developing alternative solutions. Products like Innospec's Volasil 8100 and IOTA's DM 55 can replace D4 while maintaining its performance.

Industry insiders advise that relevant companies closely monitor the progress of the US draft assessment and the timelines for various countries' bans, and implement raw material substitution and formulation adjustments in advance to mitigate cross-border trade compliance risks.