Along with collaborators at the University of California, Berkeley, I recently published a new study in Environmental Science & Technology that examines the impacts of a California law that promotes greater transparency around harmful chemicals in products. The study shows how this law is helping to shift markets toward safer products.
Under California’s right-to-know law called Proposition 65 (or Prop 65), the state of California maintains a list of around 1000 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 the listed chemicals above a specified threshold.
Influencing business decisions
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. We wanted to evaluate to what extent the law has created systems-level change (rather than changes to just individual behaviors).
We found that companies, rather than consumers, may be most affected by the law’s warning requirements, with Prop 65 influencing businesses to shift away from using toxic substances.
Impacts in California & beyond
To assess the impact of Prop 65, we conducted 32 in-depth 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. In our analysis of the interviews, we found:
- 78% of interviewees said Prop 65 has prompted businesses to reformulate their products.
- 81% of manufacturers interviewed said they look to Prop 65 to know which chemicals to avoid when formulating their products or purchasing raw materials from suppliers.
- 63% of manufacturers said that Prop 65 also drives the reformulation of their products sold outside of California.
In particular, we found that companies are very reluctant to put a label on a product that says it contains a chemical that causes cancer. This was the biggest driving force behind their decisions to reformulate.
Prop 65 also helped increase businesses’ awareness of chemicals in traditionally opaque supply chains, which assisted them in avoiding chemicals of concern in their products. We 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 prohibit Prop 65 chemicals in the cleaning products it certifies.
Motivating change
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, so that they can avoid the threat of litigation. By doing this, they reduce the risk not just to people who buy the products, but also to workers who are frequently exposed at much higher levels.
The work was part of a larger research effort to collect metrics on the impact of Prop 65 in reducing people’s exposures to toxic chemicals. In another study published last fall, my colleagues at Silent Spring and Berkeley found that levels of certain chemicals in people’s bodies went down both in California and nationwide in the years following the chemicals’ listing. This is consistent with our interview findings – namely, 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.
Effective regulation at the state level
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.
This study also gives insights into how to design effective legislation. While state bills that require ingredient disclosures are increasingly common, the language of Prop 65 warnings that explicitly link chemical exposures to health effects (for example, cancer and reproductive harm), paired with a frequently used enforcement mechanism (such as citizen suits), appears to be particularly effective at prompting manufacturers to reformulate.
Right-to-know laws can thus have broader impacts beyond increasing information transparency if designed in ways that motivate industry action.
Funding for this project was provided by the California Breast Cancer Research Program (Grant #23QB-1881) and charitable contributions to 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.
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
Jennifer Liss Ohayon, PhD is a Research Scientist at Silent Spring Institute, specializing in environmental policy, community-engaged research, and environmental justice. She is currently working on projects to report back to study participants and community partners in the U.S. and Chile their exposures to endocrine disrupting chemicals. She also researches the emergence of scientific and activist concerns around industrial chemicals with Northeastern’s PFAS lab, and, in collaboration with co-investigators at the University of California, Berkeley, is evaluating the effectiveness of California-based legislation that aims to reduce or eliminate exposures to toxic substances.