On August 31, RHP Risk Management attended the 2026 Proposition 65 Conference in San Francisco. The conference brought together the California Office of Environmental Health Hazard Assessment, the Attorney General’s Office, plaintiff and defense counsel, scientists, manufacturers, trade associations, and public-health organizations. As Proposition 65 approaches its 40th anniversary, one theme was clear: many of the program’s most challenging issues continue to center on how scientific evidence is interpreted and translated into practical decisions about products, exposures, and warnings.

Four themes were particularly relevant for companies that manufacture, import, distribute, or sell products in California.

Exposure remains the central scientific question

A Proposition 65 listing identifies a chemical as a potential carcinogen or reproductive toxicant, but the listing itself does not establish the level of exposure associated with a particular product or use. Whether a warning is required depends on how much of the listed chemical a person may actually be exposed to under reasonably foreseeable conditions of use and, where applicable, how that exposure compares with established safe-harbor levels. This distinction between hazard and exposure appeared throughout the conference: the presence of a listed chemical may trigger further evaluation, but meaningful compliance decisions require an understanding of the product, how it is used, the potential exposure pathways, and the magnitude and frequency of exposure.

A defensible evaluation starts with the product and the conditions under which people actually use it. The analysis should identify whether the listed chemical is present, how it could be released, which exposure routes are relevant, and the amount a person may receive under reasonably anticipated conditions of use. The resulting estimate can then be compared with an applicable No Significant Risk Level (NSRL) for carcinogens or Maximum Allowable Dose Level (MADL) for reproductive toxicants.

The route, frequency, and duration of exposure must align with the toxicological endpoint being evaluated. An oral study does not necessarily inform an inhalation assessment, just as a dermal exposure estimate cannot simply be applied to inhalation. Timing also matters: averaging exposure over several days may obscure a short-term peak that is more relevant when the endpoint depends on an acute exposure during a sensitive developmental window.

The period between a chemical’s Proposition 65 listing and OEHHA’s adoption of a safe harbor level can create significant uncertainty. The absence of an OEHHA value does not, by itself, answer whether a warning is required. In these situations, companies may need to conduct a product-specific quantitative risk assessment using the available dose-response and exposure data. A well-documented, transparent analysis can also position an organization to participate more effectively in OEHHA’s public process if and when a proposed safe harbor level is issued.

The exposure study must answer the actual product question

Conference discussions also underscored that data collection alone is not enough. The study design must accurately reflect the exposure scenario relevant to the product and be appropriate for the legal or regulatory question being evaluated.

For food and consumer products, this may require reliable information on typical use, high-end use, the amount consumed or applied, and the relevant population. National survey data such as the National Health and Nutrition Examination Survey can be useful when the available variables match the question. For other products, laboratory or field testing may be needed to measure emissions, airborne concentrations, dermal transfer, or the amount of a chemical released during mixing, application, maintenance, or disposal.

A strong study should document the product tested, analytical method, reporting limits, use conditions, duration, variability, assumptions, and relationship between the test conditions and foreseeable use. These details determine whether the result can support a warning decision, regulatory submission, or litigation position. Testing performed before a notice or dispute arises also gives companies more options to address uncertainty and improve the design if the first study identifies a data gap.

Warnings depend on both science and communication

The session “Modernizing Proposition 65: New Approaches to Warnings” examined how companies communicate chemical information to consumers, including digital tools such as SmartLabel. The discussion also returned to the First Amendment limits on compelled commercial speech when a warning communicates a disputed scientific conclusion.

For companies, the practical takeaway is that warning decisions should be grounded in a clear, well-documented factual and scientific record. That record should identify the chemical, product, relevant exposure scenario, applicable numerical benchmark, and the scientific basis for the conclusion. Where authoritative bodies reach different conclusions or the evidence involves meaningful uncertainty, those differences should be acknowledged and explained rather than reduced to a level of certainty the underlying science does not support.

This does not mean that every disagreement eliminates a warning obligation. It means that hazard classification, exposure assessment, dose-response analysis, and warning language should be evaluated together. Legal counsel and scientific experts need a shared understanding of what the data establish, what remains uncertain, and how that uncertainty affects the specific product decision.

Reformulation can replace one concern with another

The conference panel “BPS and Regrettable Substitution: Reformulation, Enforcement, and Fallout” focused on a recurring product-stewardship challenge: replacing a listed or closely scrutinized chemical does not necessarily eliminate risk. A substitute may present similar hazards, be supported by less complete toxicological data, or result in a different exposure profile that creates new considerations.

BPS is a useful example because it has often been used as a substitute for bisphenol A. The broader issue applies to phthalates, flame retardants, PFAS, solvents, and other chemical groups. A narrow search for a replacement molecule can become a cycle in which one regulated substance is replaced by a close analogue that later attracts the same concern.

A safer-substitution assessment should consider the candidate’s hazard profile, expected exposure, functional performance, impurities, degradation products, and available evidence. It should also ask whether the proposed replacement is one member of a broader chemical class that may be regulated together. The “least toxic alternative” may not be obvious when candidates have different hazards, exposure pathways, performance limits, and data gaps. Breakdown products deserve specific attention. A substitute that appears favorable as manufactured may create a persistent, toxic, or otherwise regulated transformation product during use, heating, weathering, combustion, or disposal. Evaluating only the parent molecule can miss the exposure that ultimately drives risk or regulation.

State chemical rules are creating a wider compliance map

The final conference session, “State vs. Federal Chemical Rules: Multi-State Momentum, Preemption, and Compliance,” examined how Proposition 65 fits within an increasingly complex landscape of state and federal chemical regulation. PFAS provided a clear example: states are adopting a range of approaches, including broad class-based definitions, reporting requirements, product restrictions, and exemptions for uses considered essential or currently unavoidable. Because these requirements can differ in how they define PFAS, which products they cover, what thresholds apply, and when they take effect, companies may face different compliance obligations for the same product across multiple jurisdictions.

Proposition 65 generally requires an exposure-based analysis, while another state law may regulate the presence or intentional addition of a chemical or chemical class. A product can therefore comply with one framework and still trigger obligations under another. Companies selling nationally need to know which rules apply to the product, which definition is controlling, and whether one formulation can satisfy the most stringent requirement without creating a new problem elsewhere.

These decisions can no longer be left to the regulatory function alone. Product development, procurement, analytical laboratories, toxicologists, exposure scientists, legal counsel, and supply-chain teams may each hold information critical to the analysis. Gaps in formulation data or unsupported supplier representations can become significant vulnerabilities when a company must later explain and defend how it reached a warning or reformulation decision.

Meet RHP’s Proposition 65 experts

RHP’s Proposition 65 work is led by board-certified toxicologists, certified industrial hygienists, and exposure scientists who publish peer-reviewed research and work these questions with clients every day.

How RHP supports Proposition 65 decisions

RHP’s Proposition 65 practice integrates exposure science, toxicology, epidemiology, analytical testing, and product stewardship. We help clients determine whether listed chemicals are present, characterize realistic exposure, compare estimates with NSRLs and MADLs, develop scientifically supportable values when an OEHHA safe harbor is unavailable, and evaluate warning, control, or reformulation options.

The 2026 conference reinforced the value of addressing these questions early. A warning decision without a clear exposure record can be difficult to defend. A reformulation decision without an alternatives assessment can exchange one liability for another. A well-documented scientific analysis gives the company, its counsel, and its technical teams a common basis for action.

Recent news & insights on chemical risk

Hover to pause · click any story to read it

This article is provided for informational purposes and does not constitute legal advice.