A new study by Silent Spring Institute and University of California, Berkeley shows how laws that promote greater transparency around harmful chemicals in products can shift markets toward safer products.
The study, published in the journal Environmental Science & Technology, focused on California’s right-to-know law called Proposition 65, or Prop 65. Under the law, the state of California maintains a list of approximately 900 chemicals known to cause cancer, birth defects, or reproductive harm. Companies that sell products in California are required to warn people if their products could expose them to harmful amounts of the chemicals.
Until recently, there has been little research on the effectiveness of Prop 65, with some critics contending the law creates too many warnings with little impact on individual behaviors, while others argue the law is less effective than those that restrict or ban chemicals outright.
“We wanted to go deeper and understand to what extent the law has created more systems-level change,” says lead author Dr. Jennifer Ohayon, a research scientist at Silent Spring Institute. “What we found was that companies, rather than consumers, may be most affected by the law’s warning requirements. By increasing businesses’ awareness of chemicals in the supply chain, Prop 65 has caused them to shift away from using toxic substances, and that’s a positive step for public health.”
To assess the impact of Prop 65, Ohayon conducted 32 semi-structured interviews with business leaders at major global manufacturers and retailers. The businesses spanned more than a dozen sectors including home improvement, clothing, personal care, cleaning, and healthcare, among others. An analysis of the interviews found:
“Companies are incredibly reluctant to put a label on a product that says it contains a chemical that causes cancer, and that was the biggest driving force behind their decisions to reformulate,” says Ohayon.
The researchers also saw impacts on the supply chain through third party “green” certification programs that have incorporated Prop 65 chemicals into their safety criteria. For instance, several major healthcare institutions said they encouraged their suppliers to use certifiers such as Green Seal, which prohibits Prop 65 chemicals in the cleaning products it certifies.
Under the law, companies can avoid triggering a warning requirement by reformulating their products to reduce the level of a Prop 65 chemical below a “safe harbor” threshold.
“What’s interesting is that companies consistently told us they would rather eliminate a Prop 65 chemical altogether than post a warning,” says co-author Dr. Meg Schwarzman, a physician and environmental health scientist at the UC Berkeley School of Public Health. “By doing that, they avoid the threat of litigation, but they also reduce the risk to consumers and workers using the products.”
The study is the first to use in-depth interviews with representatives from diverse industry sectors to understand the influence of Prop 65 on internal corporate decision-making.
The work is also part of a larger research effort to collect metrics on the impact of Prop 65 at reducing people’s exposures to toxic chemicals. In a study published last fall, the Silent Spring and Berkeley team found levels of certain chemicals in people’s bodies went down both in California and nationwide in the years following the chemicals’ listing.
Ohayon explains this is consistent with the findings from her interviews. When companies reformulate their products to comply with Prop 65, they tend to apply those changes across all of their products, not just ones sold in California.
“In the absence of federal regulations, these findings underscore the important role that states, especially large ones like California, can play in protecting the broader public from chemicals that could harm their health,” says Ohayon.
Funding for this project was provided by the California Breast Cancer Research Program (Grant #23QB-1881) and charitable contributions to Silent Spring Institute.
Reference: Ohayon, J.L., C. Polsky, M.R. Schwarzman. 2025. How a Right-to-Know Law Shifts Industry Away from Chemicals of Concern: The Case of California’s Proposition 65. Environmental Science & Technology . DOI: 10.1021/acs.est.4c07495
About Silent Spring Institute: Silent Spring Institute, located in Newton, Mass., is the leading scientific research organization dedicated to uncovering the link between chemicals in our everyday environments and women's health, with a focus on breast cancer prevention. Founded in 1994, the institute is developing innovative tools to accelerate the transition to safer chemicals, while translating its science into policies that protect health. Visit us at www.silentspring.org .
Environmental Science & Technology
Data/statistical analysis
Not applicable
How a Right-to-Know Law Shifts Industry Away from Chemicals of Concern: The Case of California’s Proposition 65
12-Feb-2025