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What are pests?

What are pesticides?

Can pesticides cause cancer?

Some people worry that being exposed to pesticides will cause cancer or ask if a pesticide caused cancer for someone they love. These are difficult questions. Many things affect the chance that a person will get cancer.

In general, no one can be sure what causes someone's cancer. It is only possible to say if being exposed increased that person's risk of cancer. In general, lowering your exposure to anything that may cause cancer will lower your risk of getting cancer.

How does exposure lead to cancer?

A carcinogen is something that scientists believe can cause cancer. Being exposed to a carcinogen raises a person's risk of cancer. The chance that being exposed to a carcinogen will lead to cancer depends on many things. It depends on the amount someone is exposed to, the length of time they were exposed to it, and how strong its effect is.

Here are some things that affect cancer risk:

1. More exposure means higher risk. Someone who smoked cigarettes for forty years has a higher chance of getting lung cancer than someone who smoked for five years. However, just because a person is exposed to something that can cause cancer doesn’t mean they will get cancer. For example, many people know someone who smoked cigarettes their whole lives and never got cancer.
2. The strength of the carcinogen matters. Different substances may have different cancer potency. Both cigarettes and processed meat (like hot dogs) are carcinogens. Scientists believe that smoking and eating processed meat both increase the risk of cancer. However, the two risks are not equal. Smoking is more likely to cause cancer than eating processed meat.
3. The type of cancer matters. Just because something causes cancer, doesn’t mean it can cause all types of cancer. For example, being in the sun without sunscreen increases the risk of skin cancer but not the risk of all types of cancer.

If I was exposed to a pesticide, will I get cancer?

"Pesticide" is a very broad term. There are thousands of pesticides. They may control insects, weeds, viruses and germs, fungi, and other pests. Some pesticides show evidence of being carcinogens, while others do not. Some pesticides have not been studied enough to determine if they can cause cancer.

The risk of cancer from a pesticide depends on if it is a carcinogen, how you are exposed, how much you are exposed to, and more. Being exposed to a pesticide that is a carcinogen does not necessarily mean you will get cancer. It only means that your risk is higher than if you were not exposed.

How do scientists study cancer risk?

Cancer is complex and studying its causes is difficult. Government agencies and groups of scientists decide if chemicals may cause cancer by looking at a variety of research. They may look at human studies, animal studies, and more.

To do human studies, researchers look at patterns of cancers and exposures in large groups of people. One strength of these studies is that they include real people. However, people are exposed to many different things during their lives and cancer can take many years to develop. This makes it hard to know how much of a chemical people were exposed to. It is also impossible to say that the chemical is the cause of a person’s cancer. This is a weakness of studies on humans.

Studies are also done on laboratory animals. A strength of these studies is that the researchers know everything the animal is exposed to. However, humans are different than laboratory animals. Therefore, it can be hard to say if people will react the same way as the animals did to a chemical. This is a weakness of animal studies.

How do I know what chemicals pose cancer risk?

Several agencies that study cancer risk have developed cancer classifications for chemicals, including pesticides. They put chemicals into these categories based on the how much evidence of cancer risk there is. Cancer classifications are not the same as the strength of carcinogen.

Examples of cancer classification categories are:

• Known human carcinogens: Researchers agree that many studies show a lot of evidence that the chemical can cause cancer.
• Possible, probable, or reasonably anticipated to be human carcinogens: Researchers find some evidence that the chemical can cause cancer, but not enough to be sure.
• Unknown or not classifiable: Researchers do not have enough information to say whether it can cause cancer. The chemical may not be studied enough or results from studies may be unclear.
• Non-carcinogenicity: Researchers don't think the chemical can cause cancer. For example, boric acid is in this category. This means scientists think that exposure to boric acid will not cause cancer. However, chemicals that do not cause cancer can still be poisonous or cause other health problems.

Pesticide databases for cancer classifications

These links have cancer classification lists created by authoritative groups:

• Chemicals Evaluated for Carcinogenic Potential – Environmental Protection Agency
• Evaluating Pesticides for Carcinogenic Potential
• California Proposition 65 Chemical List (a list of chemicals known to the State of California to cause cancer or reproductive toxicity) – California Office of Environmental Health Hazard Assessment
• National Toxicology Program, US Department of Health and Human Services
• Cancer Health Effects
• Report on Carcinogens
• IARC Monographs on the Evaluation of Carcinogenic Risk to Humans - International Agency for Research on Cancer (IARC)
• List of Classifications
• IARC Classification Categories

Last updated November 04, 2021

Understanding cancer risk can be complicated. If you have questions about this, or any pesticide-related topic, please call NPIC at 800-858-7378 (8:00am - 12:00pm PST), or email us at npic@ace.orst.edu.