You might have heard people say, “everything causes cancer.” Sometimes it feels that way when you read the news, look at certain health advice webpages, or read the labels of certain products. But the truth is more nuanced, and we do actually know about specific things that cause cancer. Most Canadians recognize that smoking and alcohol increase cancer risk, but are less good at identifying infectious diseases, red meat, or even aging. Sometimes, true causes of cancer are overlooked while misinformation gets more attention.
Myths and misconceptions about cancer causes
Some claims about the causes of cancer have stuck around for years even when there’s little or no scientific evidence behind them. For example, more than half of Canadians believe that eating genetically modified organisms (GMOs) can cause cancer, even though there is no evidence to support it. Other beliefs are more grounded in science, at least partly.
Take aspartame: around 60% of Canadians believe it increases your risk of cancer. In 2023, the International Agency for Research on Cancer (IARC) did classify aspartame as possibly carcinogenic based on limited evidence. To be sure, that sounds scary. But context matters. You’d have to drink between 9 and 14 cans of diet soda every day to reach a level that would make aspartame carcinogenic.
On the right, you’ll see a depiction of the IARC Monograph Classification System. This system classifies substances by their potential to cause cancer (hazard) based on the strength of scientific evidence available. Hazard means that the substance could cause cancer in specific circumstances, not that it will can cancer in your everyday life (that’s risk). Understanding this system can help you interpret claims in headlines or social media and make decisions about your health.
The dose and route of exposure matter.
When it comes to cancer, the key thing that determines harm is dose and route of exposure: how you’re exposed and how much you’re exposed to. Let’s look at one example: pesticides. A huge majority of Canadians – 80% of us – believe that pesticides can increase your risk of cancer. And it’s partly true! Long-term, high-level exposure to certain pesticides in agricultural settings (like for people who work on farms), may increase your cancer risk.
But when most people think about pesticide exposure, they’re thinking about the residue on fruits and vegetables. In this case, the level of exposure is well below the limit that would cause harm and there’s no evidence that eating produce treated with pesticides increases your cancer risk.
In fact, many pesticides with known harms have been banned in Canada due to their toxicity. If you are concerned about pesticides on your food, rinsing, blanching, or scrubbing your produce can remove most residue before you eat it. However you prepare them, eating fruits and vegetables does help to reduce your risk of cancer – no matter how they’re grown.
This example demonstrates a common principle you may have heard before: the dose makes the poison. Something can be harmful in large amounts or through direct exposure, but not for people in everyday life.
It’s easy to see why cancer misinformation spreads so widely.
Thinking about dose, route of exposure, risk, and hazard can be overwhelming. All of this can lead to the oversimplification of evidence, misunderstandings, or deliberate misrepresentation of the truth. But you might wonder, “why does it matter if we think things cause cancer even if they don’t?”
It’s a fair question. After all, being cautious might seem harmless. But when we focus on the wrong things, we risk missing what actually matters. Believing and spreading misinformation about cancer can cause real harm; it can create unnecessary fear, fuel distrust in science, and shift attention away from proven ways to reduce cancer risk. You can learn more about the real-world harms of cancer misinformation and how to spot the tactics of people who spread misinformation using our resources below.
Resources for the public
Discover toolkits and information about how to spot misinformation online or in the media. We also provide brief translations of our research for sharing.
Resources for healthcare professionals
Discover toolkits and information for confronting misinformation at work or with other healthcare providers.
Why is misinformation harmful?
Learn about the impacts of misinformation to individuals and the public at large.