What do carcinogen classifications actually mean?

Posted 6 Sep 2017.


Cancer is caused by changes in a cell's DNA. Some of these changes may be inherited from our parents. Others may be caused by outside exposures, which are often referred to as environmental factors or risk factors.

A carcinogen is a substance that causes cancer in the body. Many carcinogens are well known and exposure is preventable, such as asbestos or tobacco smoke. Some are less well recognised, such as alcohol.

Some carcinogens don't affect DNA directly, but lead to cancer in other ways. For example, they may cause cells to divide at a faster than normal rate, which could increase the chances that DNA changes will occur.

Carcinogens don't cause cancer in every case, all the time. Substances labelled as carcinogens may have different levels of cancer-causing potential. Some may cause cancer only after prolonged, high levels of exposure.

It's important to remember that for any particular person, the risk of developing cancer depends on many factors, including how they are exposed to a carcinogen, the length and intensity of the exposure, and the person's genetic makeup.


Carcinogen assessment system

To help everyone understand the risks associated with exposure to known, probable and possible carcinogens, a method of classification has been developed to categorise each agent and the circumstances under which exposure occurs.

These categories include:

Group 1: Carcinogenic to humans
Group 2A: Probably carcinogenic to humans
Group 2B: Possibly carcinogenic to humans
Group 3: Not classifiable as to its carcinogenicity to humans
Group 4: Probably not carcinogenic to humans


What do these categories actually mean?

Often, there can be confusion around the meaning of the carcinogen assessment system. It's important to note that the International Agency for Research on Cancer (IARC) carcinogen categorisation system refers to how much evidence there is to suggest something causes cancer, rather than how much it increases cancer risk, as is often assumed.

For example, both smoking and red meat have been classified as Group 1 carcinogens. Smoking increases your risk of developing lung cancer by 1900%. While eating 50g of processed meat per day increases your chance of developing bowel cancer by 18%1.

Therefore, while there is significant evidence to suggest that smoking and red meat both cause cancer, the level of risk associated with both of these Group 1 carcinogens is very different.

Reduce your risk

Did you know that at least a third of all cancers could be prevented by making changes to our lifestyle?

Even small changes like eating healthy, limiting alcohol consumption and ensuring you're SunSmart can reduce your risk of developing cancer.

For more information visit our reduce your risk page or give us a call on 13 11 20.



1. Slevin, T. Confused about your cancer risk from meat? The Conversation (2015).

Found in:  News - 2017  | View all news