California Prop 65 List Update: N-Methyl-N-Formylhydrazine and Bisphenol S Added

On December 5, 2025, the California Office of Environmental Health Hazard Assessment (OEHHA) announced the formal listing of two chemicals, Bisphenol S (BPS) and N-Methyl-N-Formylhydrazine, to the California Proposition 65 list. The listings are based on their respective risks for reproductive toxicity and carcinogenicity.

1. N-Methyl-N-Formylhydrazine Listed as a Carcinogen

Effective December 8, 2025, N-Methyl-N-Formylhydrazine is listed as a carcinogen. This decision followed an 8-to-1 vote by the Carcinogen Identification Committee (CIC) during its November 18 meeting, confirming that the substance is "clearly shown through scientifically valid testing to cause cancer." Businesses must provide clear and reasonable warnings for significant exposures starting December 8, 2026.

Assessment Timeline:

• November 2024 – January 2025: OEHHA solicited public input on carcinogenicity studies.
• August 29, 2025 – October 13, 2025: Released the hazard identification document and received public comments.
• November 18, 2025: CIC held a full-day meeting for deliberation, ultimately passing the listing resolution.

2. Bisphenol S Listed for Full Range of Reproductive Toxicity 

On the same day, OEHHA added the developmental toxicity endpoint to the existing listing for BPS, making it a reproductive toxicant covering female reproductive toxicity, male reproductive toxicity, and developmental toxicity. This amendment also takes effect on December 8, 2025.

Phased Listing Timeline:

• December 29, 2023: Initially listed for female reproductive toxicity.
• January 3, 2025: Added for male reproductive toxicity.
• December 8, 2025: Developmental toxicity added, completing the listing for the full range of reproductive toxicity endpoints.

Industry Impact 

The addition of these substances triggers Proposition 65's warning requirements. Businesses using these chemicals must provide clear and reasonable warnings in various locations, including on product labels and in workplaces. Failure to do so may lead to litigation risks. The complete chemical list has been updated accordingly on ChemRadar GCIS: https://www.chemradar.com/en/tools/cis/inv/64924a20e7fff39f787f1b0d

If you need any assistance or have any questions, please get in touch with us via service@cirs-group.com.

Further Information

N-Methyl-N-Formylhydrazine

Bisphenol S