Prop 65 (California Proposition 65)
Prop 65, formally California's Safe Drinking Water and Toxic Enforcement Act of 1986, requires a business to provide a clear warning before knowingly exposing a Californian to a listed chemical above its safe-harbor level — a list that runs to more than 1,000 chemicals linked to cancer or reproductive harm. It applies to any seller shipping into California regardless of where the business itself is located, which makes it a national e-commerce compliance issue rather than a California-only one. For online listings, the warning (or a clearly labeled link to one) must appear on the product's own page — a warning buried in a general policy page or checkout footer doesn't satisfy the requirement.
What triggers a warning
A warning is required when a product could expose a Californian to a chemical on the Prop 65 list above its safe-harbor level — a No Significant Risk Level (NSRL) for carcinogens or a Maximum Allowable Dose Level (MADL) for reproductive toxicants, where one has been established. Below the safe-harbor level, no warning is required even if the chemical is present in trace amounts. The list itself, maintained by California's Office of Environmental Health Hazard Assessment (OEHHA), runs to more than 1,000 chemicals and is revised on an ongoing basis, so a product that didn't need a warning last year can require one after a new listing.
It's not optional for out-of-state or online sellers
Prop 65's Section 25602(b) reaches any business that knowingly exposes a California resident to a listed chemical, with no exemption for sellers based outside the state. An e-commerce retailer with no California facility still has to warn if it knowingly ships a qualifying product to a California address — "knowingly" in practice means once notice exists, whether from a 60-day notice of violation, a retailer's own catalog requirement, or the seller's own composition data, not only after being sued.
Where the warning has to live on a listing
For an online sale, the warning must appear on the product display page itself — either the full warning text or a clearly marked hyperlink using the word "WARNING," "CA WARNING," or "CALIFORNIA WARNING." A warning that only appears at checkout, in a site-wide disclaimer, or on a separate compliance page doesn't meet the requirement; enforcement and the private-party citizen suits Prop 65 permits specifically target listings missing a page-level warning.
What this means for product data
A Prop 65 determination is effectively a Boolean-plus-text attribute at the SKU level — does this product require a warning, and if so, which chemical category triggers it. The standard "short-form" warning references broad categories like "cancer and reproductive harm" without naming the specific chemical, while a "long-form" warning does. Getting the determination into structured product data means it can be enforced consistently through syndication to every channel a SKU reaches, rather than added manually, listing by listing, after a notice arrives — which is usually how gaps get found.
Frequently asked questions
Does Prop 65 only apply to businesses located in California?
No. It applies to any business that knowingly exposes a California resident to a listed chemical above the safe-harbor level, regardless of where the seller is based — an out-of-state or online-only retailer shipping into California is in scope.
What counts as a compliant Prop 65 warning on a product listing?
The warning, or a hyperlink clearly labeled "WARNING," "CA WARNING," or "CALIFORNIA WARNING," must appear on the product's own page. A general site disclaimer or a warning shown only at checkout doesn't satisfy the requirement.
How many chemicals are on the Prop 65 list?
OEHHA's list runs to more than 1,000 chemicals as of 2026 and is updated on an ongoing basis — chemicals are added, and occasionally removed, throughout the year, so a compliance determination made once isn't permanent.
Is Prop 65 the same as a GHS or SDS hazard classification?
No — they're separate systems. [GHS](/glossary/ghs-globally-harmonized-system)/[SDS](/glossary/sds-safety-data-sheet) classify chemical hazards for handling, storage, and workplace safety under OSHA. Prop 65 is a California consumer-exposure warning law with its own chemical list, its own safe-harbor thresholds, and its own warning-label requirements; a product can require one, both, or neither depending on its composition.