Guides · US compliance
California’s Proposition 65 requires a warning before a Californian buys a product that exposes them to a listed chemical; for internet sales the regulation contemplates a warning on the product display page or a clearly marked hyperlink before purchase. On Amazon, sellers routinely conclude the warning system is broken, because they fill in the attribute and see nothing appear. Everything below was measured on real product pages in August 2026, and the two facts that resolve the confusion are: the warning is composed from your attribute, and it renders only when the shopper’s delivery address is in California.
The rendered warning is not your listing copy echoed back. Amazon composes
it from two attributes — california_proposition_65_compliance_type and
california_proposition_65_chemical_names — substituting the chemical
name exactly where the selected warning type permits one and omitting it exactly where
that type forbids one. Three products, three different attribute values, three different
statutory templates rendered:
| Attribute selection | What renders on the detail page |
|---|---|
| Chemical type, both endpoints, chemical names filled (lead) | The full-form warning naming “lead and lead compounds”, cancer and reproductive harm, ending in the P65Warnings.ca.gov reference. |
| Chemical type, reproductive endpoint, chemical named (BPA) | The full-form warning naming bisphenol A, reproductive harm only. |
| On Product Combined Cancer and Reproductive | The short form: “WARNING: Cancer and Reproductive Harm” plus the reference — and no chemical name, because Amazon’s own table for that row says you may not select one. |
The warning appears on the detail page as a link whose visible text is the single word WARNING, beside “California’s Proposition 65”; the full statutory sentence sits one click behind it. The page slot exists on every product page we measured — on products with no warning, the slot is present and empty, which means an empty slot is a seller who never populated the attribute, not a page layout that lacks the feature.
The same product pages were measured twice, changing only the shopper’s delivery address. This is the whole confusion in one table:
| Product | Delivery address Georgia | Delivery address Los Angeles |
|---|---|---|
| Lead fishing sinkers | No Proposition 65 text anywhere in the page HTML | Warning renders |
| Vinyl garden hose | None | Warning renders |
| 50-foot extension cord | None | Warning renders |
A seller who checks their own listing from Texas, Florida or Georgia sees no warning, concludes the attribute did nothing, and either files a ticket or starts pasting warning text into the description — the exact move Amazon prohibits (next section). Before concluding anything about your Prop 65 setup:
Open your product page → set the delivery location to a California ZIP (90001 works) → reload → look for the WARNING link in the legal section above the product description.
Whether the linked warning discharges your own duty to the consumer is a legal question for your counsel; what is measured here is only where the warning comes from and who is shown it.
Amazon’s seller help on Prop 65 (article G202141960) is unusually direct. It instructs sellers to provide the warning through the attribute instructions on that page “and not in any other way, such as by email”, and separately not to send warning materials — labels, labeling, shelf signs or tags — to display with the product unless Amazon instructs it in writing. Two consequences:
The compliance-type field is an enum with eleven values, and eight of them forbid a chemical name; the short-form rows say outright that you may not select one. So the two attributes must agree: a short-form type with a chemical name filled in is a contradiction, and a Chemical type with the names field empty is an incomplete warning. Check the pair together, not one field at a time. If no Proposition 65 warning applies to your product at all, clear the declaration rather than leaving a half-filled pair.
OEHHA amended the short-form warning rules effective January 1, 2025: new-style short-form warnings name a chemical, and the old chemical-free short form (“WARNING: Cancer and Reproductive Harm”) is permitted on products manufactured before January 1, 2028. The short form Amazon renders from the combined type today is the legacy format riding that transition window. Amazon’s own public explainer describes the 2025 expansion and the 2028 deadline; expect the warning-type table to change shape before then, and treat any listing relying on the chemical-free short form as one with a known expiry date on its current wording.
The warning is one attribute pair on one marketplace. The listing-level question is whether each row of your catalog carries what the platform’s checks read — declarations that agree with themselves, compliance documents, and copy free of the wording that triggers removal. Pronoia reads those from your own listings export, including the Prop 65 declaration pair, and treats statutory warning text as compelled speech rather than as a marketing claim. Drop the file on the scan page and it is scored in your browser, nothing uploaded, or email it to audit@trypronoia.com for an audit, free for our first sellers, one each.