Glossary
Prop 65
California's Proposition 65 requires a clear warning on products sold in California if they expose users to any of the hundreds of chemicals the state has listed as causing cancer or reproductive harm, above set thresholds.
Why it matters
Prop 65 is a California state law, not a federal one, but because products circulate nationally it effectively governs labelling for most physical goods sold anywhere in the US, and it is enforced heavily through private citizen lawsuits rather than only by regulators.