ALETHEIA  /  Resources  /  California Prop 65 Marketplace Compliance Guide

What's inside

• The OEHHA Prop 65 list — ~900 chemicals as of December 2025, the four pathways for new additions, why the list is structured the way it is.
• NSRL and MADL — the safe-harbor math that determines whether a warning is required at all. NSRL = 1 excess cancer per 100K over 70-year lifetime exposure; MADL = NOEL ÷ 1,000.
• The 30 chemicals marketplaces actually deal with — full table with CAS numbers, listing endpoint (cancer / reproductive / both), and where each shows up in seller listings.
• 2025 short-form warning amendments — what changed (chemical name now required), the 3-year grace period, the Jan 1, 2028 hard deadline.
• Online & marketplace warnings — the four acceptable methods (display-page text, "WARNING"-labeled hyperlink, California-ZIP pop-up, interstitial), with the exact-text rules for hyperlink labels.
• The 60-day pre-suit notice playbook — five concrete operational steps to use the window correctly + the three postures most marketplaces take and which one wins.
• Three approaches to programmatic screening — build, license a Prop-65-specific database, or use a cross-agency consensus API. Honest tradeoff analysis for the Prop 65 vertical specifically.
• Pre-flight compliance checklist — for product creators + for marketplace operators, with the warning-method options + the audit-trail discipline that's required to defend an action.
• Resources + every primary statute/regulation cited — verifiable against California Legislative Information + 27 CCR + OEHHA without a second source.