Coffee shops in California have been ordered to post warnings that the coffee they sell can cause cancer. Not that it does—there is no scientific evidence of risk, surely not enough to warn against it. But in the eyes of California law, the microscopic existence of a specific chemical in coffee beans suffices to require a warning.

The law is a thirty year old California rule known as Proposition 65. It requires companies selling products that expose people to cancer risk to post warnings of such exposure. If a product contains any substance that appears on California’s carcinogenic list, the company has to prove that the existence is harmless or else post the warning notice. One of the substances on the California list of carcinogens is Acrylamide.

When roasted, coffee beans emit the pernicious acrylamide (common also in many other foods), which—in significant dosage—can be toxic, and even carcinogenic. In coffee, however, it appears in such small amounts that no reliable scientific study has shown it to pose a meaningful danger. Acrylamide’s presence in coffee is not meaningfully greater than that in other daily foods such as toast, potato chips, or black olives.

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