The effect of lifestyle on some non-communicable diseases: Carcinogens, including ionising radiation, as risk factors in cancer.

The idea

A carcinogen is any agent that increases the chance of cancer developing by damaging DNA, so cells may divide in an uncontrolled way and form a tumour. Ionising radiation is a physical carcinogen: its high-energy waves or particles can break chemical bonds in DNA, producing mutations. Sources include X-rays, gamma rays, and radon gas. Other carcinogens include ultraviolet (UV) light (which is non-ionising), tobacco smoke, asbestos and some chemicals. Risk means probability, not certainty: exposure raises the chance of cancer but does not guarantee it, and risk generally increases with dose and duration of exposure.

What earns the marks

• Defines a carcinogen as an agent that increases the risk of cancer, typically by causing mutations in DNA.
• Identifies ionising radiation as a physical carcinogen that can damage DNA because it carries enough energy to break chemical bonds.
• Gives named sources of ionising radiation, such as X-rays, gamma rays or radon gas, and distinguishes these from non-ionising carcinogens like ultraviolet light.
• Explains that mutations may lead to uncontrolled cell division and tumour formation.
• States that risk depends on factors such as dose, duration and frequency of exposure, and that exposure raises probability rather than causing cancer with certainty.
• Compares carcinogens with other risk factors, for example genetic inheritance, age, smoking or diet, and explains how reducing exposure can lower risk.

Common mistakes and how to put them right

• Saying that a carcinogen definitely causes cancer in anyone exposed.

  Put it right: It increases the probability of cancer, and other factors also contribute.

• Confusing carcinogens with mutagens or teratogens.

  Put it right: Carcinogens increase cancer risk, often by causing mutations, but the terms are not interchangeable.

• Classifying ultraviolet light as ionising radiation.

  Put it right: UV light from the Sun is a carcinogen but it is non-ionising, whereas X-rays, gamma rays and radon gas are ionising.

Exam tips

• Link the carcinogen to DNA damage and then to uncontrolled cell division, so the explanation forms a logical chain.
• Use the word risk rather than cause, and mention dose or duration to show understanding of probability.
• When asked to compare, give one similarity and one difference between a carcinogen and another risk factor, using named examples.