Coffee will now come with a cancer warning in California. Here’s why the state puts warnings on more than 1,000 foods, places, and chemicals.

You can't park a car indoors in the Golden State without seeing a warning about the ways your cancer risk might spike.

Earlier this week, a California judge ordered that all coffee sellers in the state must post warnings about the potentially cancer-causing effects of a chemical in coffee called acrylamide.

Acrylamide occurs naturally in small quantities when coffee beans — and many other plant-derived foods — are roasted, though research suggests the health benefits of drinking coffee vastly outweigh the risks.

California's warning rule comes from a 1986 state law called Proposition 65, which was enacted to protect California's drinking water supply from toxic, potentially cancer-causing chemicals. But the law also mandates that the state keep a master list of all chemicals known to be toxins, and requires manufacturers and businesses to warn people about these chemicals if they're present in products or buildings (even in extremely small doses).

There are more than 1,000 chemicals on California's cancer-warning list, which grows every year. Some chemicals on it have been proved to cause cancer, but not all. A chemical needs to have only a one in 100,000 chance of upping your risk for cancer to merit a written warning to consumers.

As the American Cancer Society says on its website: "The Prop 65 labels only tell you that a product has something in it that might cause cancer or affect reproduction. They don’t say what the substance is, where it is in the product, how you might be exposed to it, what the level of risk is, or how to reduce your exposure."

Parking your car in an indoor, enclosed parking deck

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Drinking coffee

California now warns all residents that a cup of joe might cause cancer, but scientists aren't so sure.

Researchers who've studied coffee drinkers for years think that those people probably aren't at any higher risk of getting cancer. Instead, caffeine addicts may actively lower their risk of developing some kinds of cancers, including oral, prostate, and liver cancer.

But those findings didn't stop a California judge from ruling that coffee might be associated with a risk of cancer because it contains a tiny dose of a chemical called acrylamide. The compound can form when food is cooked at high temperatures, through processes like frying, baking and roasting. Acrylamide has been linked to cancer in mice and rats when it's put in their drinking water, but only in very high doses.

Acrylamide is in all kinds of cooked food we regularly eat, like french fries, potato chips, cookies, and cereal. There's no evidence yet that the amount of acrylamide in a cup of coffee has any detrimental health effects. In fact, you'd have to drink in thousands of times the amount of acrylamide in a cup of coffee to get to those levels. It's much more likely that acrylamide in cigarettes could be worrisome for people.

Still, places like Starbucks (pictured above) have started pinning up signs to comply with the new California regulation.

Being on your phone

Phones aren't chemicals, so they're not on the official Prop 65 list, but the California Department of Health still warns that the radio frequency energy they emit might cause cancer.

Scientific studies haven't demonstrated that cellphone radiation levels are anything to worry about in humans yet, though researchers have noticed some worrisome tumor growth and heart tissue damage in rats who were exposed to cellphone radio frequency radiation, as Science Friday recently reported. The scientists weren't, however, able to replicate those effects in mice.

California residents are told not keep their phones in their pockets, and to store them away from the bed at night. The health department also suggests consumers use wired headphones, wireless headsets, and speakerphone capabilities instead of holding their phone up to their ear, and send more texts to avoid keeping phones close to their heads.

Staying at a hotel

Even spending a little time as a tourist in California can up your cancer risk, the state says.

"When you check in at a hotel, look for a Proposition 65 warning sign at the hotel’s check-in desk, or a warning printed on the registration form," the state suggests, adding, "if you have any questions about the warning, ask hotel representatives."

Not all hotels have the cancer warnings — much of the danger the state is worried about in hotels comes from toxins in substances like secondhand smoke or alcohol.

Drinking and smoking are both activities that are known to increase your risk of developing cancer, so California suggests choosing smoke-free hotels and avoiding the smoking areas.

Going to your dentist's office

Even getting your teeth worked on can be risky, according to California's warning system: Some chemicals on the state's list are used in common dental procedures.

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Having a bite to eat in a restaurant

Going out to eat is not a cancer risk-free activity either, according to California.

Any place that serves fries, alcohol, or some balsamic vinegars that may contain lead must also serve up this warning to customers:

Enjoying a day at an amusement park

Amusement parks aren't all fun and games, according to Prop 65.

The state cautions that exhaust from rides, lead in railings, secondhand smoke from fellow park-goers, and greasy food could all raise cancer risk.

It's true that the chemicals in all of those things have been shown to be linked with higher rates of cancer, but you'll find all of them outside of amusement parks, too.

Drinking alcohol

Even if some of California's cancer warnings seem silly, others are very sound.

Scientists have known for years that the more alcohol you drink, the higher your risk may be of developing cancers like throat, liver, breast, and colon.

Cancer doctors in the US say even as little as one glass a day of an alcoholic drink can contribute to your risk of developing cancer.

California cancer warnings can give people the sense that just about anything they do might cause cancer.

The Los Angeles Times editorial board outlined how useless the state's warnings can be in a September opinion piece.

"The signs they post don't provide the context to help people make educated decisions about the risk they face," the board wrote. "Many don't even identify which chemical or chemicals are at issue."

New rules set to be in place by August 30 will require companies to name at least one risky chemical in any product that comes with a cancer warning. Warnings will also have to include a note telling consumers the URL of the state's website, where people can find more information about how to reduce their exposure to toxic chemicals.

With those changes, California's ubiquitous cancer warnings may at least get a bit more helpful and specific.

Coffee will now come with a cancer warning in California. Here’s why the state puts warnings on more than 1,000 foods, places, and chemicals.

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