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Cancer Risk and Prevention

Cancer Warning Labels Based on California's Proposition 65

Labels warning that a product contains chemicals that may cause cancer, birth defects, or reproductive harm are now required on many household items sold in California. But people all over the country might see them because many companies put the labels on all items that contain these chemicals, even if they’re going to be sold in other states. The warning labels can be found on many kinds of products, such as electrical wires, jewelry, padlocks, dishes, flashlights, and pesticides, to name just a few.

What is proposition 65?

California’s Proposition 65, also called the Safe Drinking Water and Toxic Enforcement Act, first became law in the state in 1986. It is intended to help Californians make informed decisions about protecting themselves from chemicals that could cause cancer, birth defects, or other reproductive harm.

As part of the law, the state is required to publish a list of chemicals that are “known to the State of California to cause cancer or reproductive toxicity.” The list is updated at least once a year and now contains more than 900 different chemicals. The complete list can be found on the California Office of Environmental Health Hazard Assessment (OEHHA) website at

There are several ways a substance can be added to the OEHHA list. One way is if it’s considered by an ‘authoritative body’ to cause cancer in humans or lab animals. Organizations designated as authoritative bodies by the state of California include the International Agency for Research on Cancer (IARC, which is part of the World Health Organization), the US National Toxicology Program (NTP), and the US Environmental Protection Agency (EPA), among others. (To learn more about these organizations and what they do, see Determining if Something Is a Carcinogen.) The State of California can also make its own determinations about specific substances.

Not all of the cancer-related substances on the OEHHA list are considered to be known human carcinogens (known to cause cancer in people) by the organizations above. This means that not every chemical on the list has been proven to the worldwide scientific community to actually cause cancer in people.

When are labels required?

As part of the law, most businesses  selling products in California must provide “clear and reasonable warnings” before knowingly exposing people to any chemical on the list, unless the expected level of exposure would pose no significant cancer risk. This warning is often in the form of a label on the product or its packaging.

The law defines “no significant risk” as a level of exposure that would cause no more than 1 extra case of cancer in 100,000 people over a 70-year lifetime. So a compound doesn’t have to be labeled if a person exposed to the substance at the expected level for 70 years is estimated to have less than a 1 in 100,000 chance of getting cancer due to that exposure. The law also has similar strict cutoff levels for birth defects and reproductive harm.

Businesses decide whether to put warning labels on their products based on their knowledge of the types of chemicals in them.

What the labels say and don’t say

For any product made after August 2018, the Prop 65 labels typically say something like this:

WARNING: This product can expose you to [name of chemical], which is known to the State of California to cause cancer. For more information, go to

Businesses are not required to use this exact wording (as long as it still provides a “clear and reasonable warning”), so it can vary somewhat between labels.

Prior to August 2018, businesses didn’t have to specify which chemical(s) of concern were in their products, so any products made before this date might not list any specific chemicals. As of August 2018, the label should name at least one chemical of concern. The label doesn’t have to list all of them, although the business might choose to do so.

Some types of products are required to have specific labels as a result of court orders after lawsuits. For example, the required labels on electrical wires such as computer cables, power cords, and holiday lights sold in California are slightly different. (This is discussed below.)

The Proposition 65 warning labels might cause some confusion for people who see them, for a few reasons:

  • The label only tells you that a product has a chemical (or chemicals) in it that might cause cancer (or affect reproduction). The label isn’t required to list every chemical of concern (if there’s more than one). And before August of 2018, the labels didn’t need to list any chemicals by name.
  • The label doesn’t have to say anything about how much of the chemical(s) the product contains, or how you might be exposed to it. These factors can be very important when determining how much risk it might pose.

How to get more information about what’s in the product

While businesses are required to put warning labels on products, they’re not required to list all of the chemicals that might cause problems, nor are they required to provide the OEHHA with any information about the products. This means the OEHHA cannot offer information to help consumers figure out what the potential risk is with a specific product or how to avoid it.

If you find a warning label on a product and want more information:

  • Find the name of the manufacturer by checking the package and any written information that comes with the product. The contact information is often on or in the package as well, but if it isn’t, you can look it up online by searching the manufacturer’s name.
  • Contact the manufacturer to find out what potentially hazardous substance(s) the product contains. You might also want to ask what part of the product it’s in.
  • Ask the manufacturer how a person might be exposed to the chemical(s) of concern from this product. Some common exposure routes include inhalation, contact with food, transfer to food or drink from unwashed hands, or a baby or child putting the product in their mouth. Different routes are important for different substances.
  • Find out what the manufacturer knows about the hazards of the chemical(s) in the product. Do the risks include cancer, reproductive harm, or both?
  • Ask the manufacturer if there are ways to reduce any risk of exposure to the hazardous substance while using the product.

Once you know which chemical(s) the product contains, you can usually find more information about it from other sources. For example, the OEHHA has fact sheets on many common chemicals on its website at Sometimes you can find information on specific products on the OEHHA website as well.

Unlabeled products

Products that are sold outside of California are not required to have the warning label even if they contain substances that might cause cancer. Some companies that sell products all over the US only label those sent to California, even though all their products contain the same compounds.

Labels on lead-containing wire

The required labels on electrical wires such as computer cables, power cords, and holiday lights sold in California are slightly different from the labels on other products, and typically say something like this:

WARNING: Handling the cord on this product will expose you to lead, a chemical known to the State of California to cause [cancer, and] birth defects or other reproductive harm. Wash hands after handling.

The word “cancer” (in brackets above) is optional, at the judgment of the manufacturer. Many of them use it, possibly to avoid liability.

Lawsuits filed in 2000 charged that electrical manufacturers were selling covered electrical wires and cable products in California without labels, despite the fact that the wires and cables had lead in their coverings. (Lead is a substance on the California list.) As part of the lawsuit settlement, manufacturers were directed to start putting warning labels on electrical cords as of late 2003. People who buy new electrical products are often concerned when they see these warning labels, but cords have contained lead for many years. Only the labels are new.

Cords that are not often plugged and unplugged do not have to be labeled. Cords with lead inside their covering, and cords that are in places that make them inaccessible to consumers during ordinary use do not have to be labeled.

More about cancer warning labels that mention California

For more information and frequently asked questions about Proposition 65, go to:

Proposition 65 is reviewed in plain language at:

For a fully updated list of all the chemicals that are known to the State of California to cause cancer or reproductive toxicity, go to:

Fact sheets for some of the chemicals on the list are available at:

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.

California Office of Environmental Health Hazard Assessment. New Proposition 65 Warnings. Accessed at on May 6, 2019.

California Office of Environmental Health Hazard Assessment. Proposition 65 Clear and Reasonable Warnings Questions and Answers for Businesses. Accessed at on May 6, 2019.

California Office of Environmental Health Hazard Assessment. Frequently Asked Questions. Accessed at May 6, 2019.

Last Revised: June 26, 2019

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