Fall 2025

You’ve Been Warned: How an Understanding of Toxicology Informs California Proposition 65 and Other Food Warning Label Regulations

By Steven Boomhower, Ph.D.

Across the United States (US), there has been a renewed interest in regulations addressing consumer warnings on food.  In June 2025, both Texas and Louisiana passed laws that would require food products containing one of over 40 listed ingredients to bear a warning label (Texas, State Legislature, 2025; Louisiana, State Legislature, 2025) (see Table).  Additionally, older related state laws, such as the California Safe Drinking Water and Toxic Enforcement Act of 1986 (better known as “California Proposition 65”), continue to expand the list of chemicals that could necessitate warning labels on foods.  For example, the California Proposition 65 list now includes over 900 chemicals, up from approximately 40 chemicals on its initial list (CalOEHHA, 2025).  Such state laws are thought to reflect a trend of increased scrutiny of food products, particularly in light of the May 2025 “Make America Healthy Again (MAHA)” assessment (Executive Office of the President of the United States, 2025).  Although each law has differences – what should be included on warnings, the chemicals of interest, whether exposure should be considered – many regulations that require food warning labels necessitate an understanding of toxicology and risk sciences.

Louisiana, Texas, and California Food Ingredient Warning Label Regulations

For several regulations, the decision to list a particular chemical as meriting a warning label for food products may be driven, in part, by an authoritative agency’s evaluation of the toxicity of the chemical.  For example, the US Environmental Protection Agency (US EPA), US Food and Drug Administration (US FDA), and International Agency for Research on Cancer (IARC) are three examples of “authoritative bodies” whose toxicological reviews are used to list chemicals under California Proposition 65 as causing cancer or reproductive toxicity.  Under the new Texas law, toxicological reviews from agencies in Australia, Canada, the European Union (EU), and the United Kingdom (UK) appear to be the drivers for listing a chemical that is not recommended for human consumption (Texas, State Legislature, 2025).  (A provision under the new law, however, eliminates the need for a warning label if the US FDA or US Department of Agriculture [USDA] determines the listed ingredient or class of ingredients is safe for human consumption.)  Thus, food manufacturers and other stakeholders should understand:  the scientific basis for an agency’s determination that a chemical is a potential health hazard; whether such a health hazard is expected to arise from oral exposure; and whether the basis reflects the current state of the science.

An important consideration in assessing the scientific accuracy of a warning label is the concept of the dose-response relationship, which means only exposure above a sufficient dose and duration would be associated with a particular health effect.  Often, information on the dose and duration necessary to pose a health risk is absent from warnings.  For example, a full-length warning under California Proposition 65 may state, “Consuming this product can expose you to [chemical], which is known to the State of California to cause birth defects or other reproductive harm” (CalOEHHA, 2025).  For this type of warning, exposure assessments are informative and can estimate “typical” scenarios related to the expected consumption of the food item in a target population, or utilize exposure modeling to predict whether the chemical would reach a particular threshold concentration in biological samples (e.g., blood or urine) in consumers.  Under California Proposition 65, some guidance is provided for certain exposure assessments, such as target population characteristics, exposure assumptions, and relying on “average” (rather than extreme or excessive) use of a product.  However, other state regulations, including the new Texas and Louisiana laws, generally do not describe how or whether exposure assessment should be used in evaluating compliance with warning label requirements.

Exposure limits are derived to estimate the dose at which no adverse effects are expected to occur, often with the application of a safety (or uncertainty) factor to err on the side of caution.”

Furthermore, health-based exposure limits for particular food ingredients may be important for interpreting the accuracy or necessity of food warning labels.  Exposure limits are derived to estimate the dose at which no adverse effects are expected to occur, often with the application of a safety (or uncertainty) factor to err on the side of caution.  At times, exposure limits are used, in part, to support a warning exemption.  For instance, under California Proposition 65, a warning is not required if the estimated exposure to the listed chemical for a typical consumer is equal to or less than a “safe harbor limit.”  Sometimes updated scientific information, on a chemical’s kinetics or its mode of action, for example, can be used to reduce uncertainty in exposure limits for food additives or ingredients.  Toward this end, my colleagues and I recently conducted a mode-of-action analysis to support the derivation of an updated acceptable daily intake of propylene glycol, a common food and beverage additive (Lewis et al., 2024).  Under the new Texas and Louisiana laws, “lactylated fatty acid esters of glycerol and propylene glycol” appear on the list of ingredients requiring a warning, despite multiple health agencies, including the European Food Safety Authority (EFSA), having health-based exposure limits for propylene (Texas, State Legislature, 2025; Louisiana, State Legislature, 2025).  As states continue to expand warning label requirements for certain chemicals in food, an understanding of toxicology, exposure assessment, and health-based exposure limits is important for ensuring that such regulations are both protective of public health and reflect the current state of the science.