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Harmful substances - chemicals, pollution and cancer

Environmental pollution accounts for a relatively small number of cancer deaths. Every day, we are exposed to thousands of different chemicals, many of which are man-made. If you are worried that these chemicals may be harmful to your health, you are not alone. But are synthetic chemicals really as bad for you as some people believe? Can they cause cancer, or are such worries unfounded?

A small effect

For most people in the UK, harmful chemicals and pollution pose a very minor risk.

Some of these can indeed increase the risk of cancer, including asbestos, and some industrial chemicals. But they are in the minority and only cause a small proportion of all cancers.

Large organisations like the World Health Organisation (WHO) and the International Agency for Research into Cancer (IARC) have estimated that pollution and chemicals in our environment only account for about 3% of all cancers.

Most of these cases are in people who work in certain industries and are exposed to high levels of chemicals in their jobs.

Lifestyle factors such as smoking, alcohol, obesity, unhealthy diets, inactivity and heavy sun exposure account for a much larger proportion of cancers.

*Avoiding health scares

There have been many health scares about cancer-causing chemicals in recent years. Often these begin when laboratory tests show that a common chemical can cause cancer. But these tests can be misleading because:

  • they are often done using individual cells or rats. Harmful effects that are discovered in cells or rats do not always apply to people.
  • they often use much higher doses of chemicals than a person would encounter.

For example, high levels of some pesticides have been shown to cause cancer in animals. Because of this, some people worry about eating fruit and vegetables, which may have traces of pesticides on them. But these trace levels are very low and unlikely to affect your risk of cancer.

Dangerous chemicals may not be dangerous at very small doses. Dose is important

Many of the chemicals that we are exposed to might be harmful at a much higher dose, but are relatively safe at low doses. In fact, almost everything is dangerous at a high enough dose, including water and oxygen.

There is a big difference between showing that something can cause cancer at high doses in cells or animals, and showing that it can do the same at low doses in people.

Organisations such as the Food Standards Agency (FSA), and the Department for Environment, Food and Rural Affairs (DEFRA) are responsible for monitoring the chemicals in our environment. They test these substances to see if they are safe and check that they are present in harmless amounts.

In this section...

This section has more information about some known harmful substances including:

And our Cancer controversies and Food controversies sections have more information about unproven chemical cancer risks such as:

The most important source of dangerous chemicals

A single source of dangerous chemicals is responsible for more than a quarter of all cancer deaths in the UK - tobacco.

Tobacco smoke contains over 70 different cancer-causing chemicals. When you smoke, your lungs and other organs absorb high concentrations of these chemicals into your body. And passive or second-hand smoke can contain even more of these chemicals than the smoke that gets inhaled.

In smokers, the effects of these chemicals far outweigh any other exposures they may experience. For example, benzene is a nasty cancer-causing chemical used in manufacturing industries and found in car exhausts. But smoking is the major source of benzene exposure in the general population. In the US, it accounts for half of people’s benzene exposure.

The best ways to reduce your exposure to cancer-causing chemicals are to avoid starting smoking or to give it up.

Dioxins are an unintentional by-product of industrial processes. Dioxins

Dioxins are a group of chemicals that are formed unintentionally by industrial processes such as burning fuels and incinerating waste. Because they do not break down easily, dioxins can persist in the environment and accumulate in the food chain. Most of our exposure to dioxins comes from our diet, especially from meat.

The term ‘dioxin’ refers to a wide range of related chemicals that can have negative effects on our health. But only one of these, known as TCDD, has been shown to cause cancer in people.

Some studies have found that people who eat highly-contaminated foods or who were accidentally exposed to TCDD at work had higher risks of cancer. But in general, people are exposed to concentrations of TCDD that are 100-1000 times lower.

Our exposure to dioxins has halved since the early 1990s and currently falls within the World Health Organisation’s recommended guidelines. They are likely to drop even further due to better monitoring and controls by the food industry.

Breast-fed children are exposed to higher levels of dioxins. But the benefits of breastfeeding (including a reduced risk of breast cancer in the mother) far outweigh these risks.

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Updated: 25 September 2009