What a California Proposition 65 Cancer Warning Actually Means

The sign on the parking garage

You have seen it. A yellow triangle with a black exclamation point, the word WARNING, and a sentence about cancer. It is on garages, hotel lobbies, extension cords and coffee shops.

Most people read it as a claim about the product. It is not. It is a claim about a list, and about a legal threshold. Those are different things, and the gap between them is worth ten minutes.

What the law says

Proposition 65 is the Safe Drinking Water and Toxic Enforcement Act of 1986. California voters passed it on November 4, 1986, and it took effect on January 1, 1987.

The core rule is one sentence. Health and Safety Code 25249.6 says no business shall knowingly and intentionally expose anyone to a chemical known to the state to cause cancer or reproductive harm without first giving clear and reasonable warning.

Section 25249.8 sets up the list. A chemical goes on it if the state's qualified experts find it has been clearly shown to cause cancer through valid testing, or if a body those experts consider authoritative has formally identified it that way, or if a state or federal agency already requires it to be labeled as causing cancer. The list is republished at least once a year.

Hazard is not exposure

This is the part that gets skipped, and it is the whole thing.

Listing answers one question. Can this chemical cause cancer at some dose, in humans or in animals? A chemical that causes tumors in rats at high doses can be listed. So can one linked to cancer in workers exposed daily for decades.

Warning answers a different question. Are you being exposed to enough of it to matter?

The law sets that bar in section 25249.10. A business does not have to warn if it can show the exposure poses no significant risk at lifetime exposure. The burden of proving that sits on the business.

And the regulations put a number on "no significant risk." Under 27 CCR 25703, it is the level calculated to result in one extra case of cancer in an exposed group of 100,000 people, assuming exposure at that level for a lifetime.

Read that again. One in 100,000, over a lifetime, is the line. It is set low on purpose.

So a warning does not mean you are near a dangerous dose. It means a business concluded it could not show the exposure sits under that very low bar. Or it means the business posted a sign without doing the analysis at all, which nothing in the law prevents.

What the sign has to say

The warning rules in Article 6 took full effect on August 30, 2018.

Under 27 CCR 25603, a consumer product warning that qualifies for the regulatory safe harbor needs three things: a black exclamation point in a yellow triangle, the word WARNING in bold capitals, and a sentence naming at least one chemical, plus the state website.

The regulation spells out the sentence. "This product can expose you to chemicals including [chemical], which is known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov."

Naming the chemical is the useful change. It gives you something to look up. A warning about lead in a ceramic mug and a warning about acrylamide formed when potatoes are fried describe very different situations.

The coffee rule

In 2019 California wrote a regulation that says the quiet part out loud.

27 CCR 25704 states that exposures to listed chemicals in coffee, created by roasting the beans or brewing the drink, do not pose a significant risk of cancer. It was filed on June 3, 2019 and took effect that October.

Coffee does contain listed chemicals formed during roasting. The state still concluded that drinking it does not carry a significant cancer risk from them.

That is the lesson in one product. A listed chemical being present is the start of a question, not the answer.

When to get checked

A warning label is not a symptom, and there is no test for "I saw a sign." What is worth acting on is different.

For people who feel well, screening runs on ages. Colorectal screening starts at 45. Cervical screening starts at 21. Mammograms are discussed from 40. A yearly low-dose CT is for adults 50 to 80 with a 20 pack-year smoking history who smoke now or quit within 15 years. Our guide to screening by age sets out the schedule.

Symptoms are a separate track and do not wait for a screening date. Blood in the stool or urine, a lump that persists, unexplained weight loss, a cough or hoarseness lasting weeks, bleeding between periods or after menopause, or a mole that changes all need an appointment.

What this does and doesn't change

• A warning is not a measurement. It does not tell you the dose, and it does not tell you whether your own exposure crosses the threshold.
• No warning is not a clean bill of health. Exposure may be below the bar, or the business may be exempt, or federal labeling law may preempt the state rule.
• Prop 65 is California law. National products often carry the sign everywhere, because one label is cheaper than two.
• The list flags hazards. It does not rank them. Two chemicals on it can differ enormously in real-world risk, and the list does not say which is which.

NCI's own list of established cancer risk factors is short and does not match what is on warning labels. It names tobacco, alcohol, sunlight, obesity, diet, infectious agents, radiation, chronic inflammation, hormones, immunosuppression, cancer-causing substances and age.

Some of those you can change and some you cannot. But if a yellow triangle has you worried, our pages on tobacco, UV radiation and medical imaging radiation are a better use of the same worry.

Sources

• California Health and Safety Code 25249.6, Required Warning Before Exposure — https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HSC&sectionNum=25249.6
• California Health and Safety Code 25249.8, List of Chemicals Known to Cause Cancer or Reproductive Toxicity — https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HSC&sectionNum=25249.8
• California Health and Safety Code 25249.10, Exemptions from Warning Requirement — https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HSC&sectionNum=25249.10
• 27 CCR 25603, Consumer Product Exposure Warnings: Content — https://www.law.cornell.edu/regulations/california/27-CCR-25603
• 27 CCR 25703, Quantitative Risk Assessment — https://www.law.cornell.edu/regulations/california/27-CCR-25703
• 27 CCR 25704, Exposures to Listed Chemicals in Coffee Posing No Significant Risk — https://www.law.cornell.edu/regulations/california/27-CCR-25704
• OEHHA, Proposition 65 Clear and Reasonable Warnings: Questions and Answers for Businesses — https://oehha.ca.gov/media/downloads/crnr/art6businessqa.pdf
• NCI, Risk Factors for Cancer — https://www.cancer.gov/about-cancer/causes-prevention/risk

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

The National Cancer Information Foundation publishes Cancer Explained. This page is for learning. It is not medical advice and does not suggest a test or treatment.

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