Faculty of Science

Department of Chemistry
Cancer is a disorder of cells in the body. It begins with a group of cells that fail to respond to the normal control mechanism and continue to divide without need. The new growths are called tumours or neoplasia and may be either "benign" or "malignant". A "benign" tumour is one that remains localised whereas "malignant" tumours invade neighbouring tissues, enter

blood vessels, lymphatic vessels and other spaces and can be carried to other areas of the body to form new tumours called "secondaries" or "metastases".

Cancer carries with it a high risk of premature death.

Cancer may arise from various causes, one of which is the adverse effects of certain substances on the cells of the body either directly or via their metabolites. While it is often difficult to prove a causal link between exposure to a certain chemical and subsequent cancer, there exists evidence to incriminate a number of compounds and other are under more or less strong suspicion. Several organisations and bodies provide lists of known or "suspect" carcinogens, classified into different categories and some of these are covered here.


Under the UK Control of Substances Hazardous to Health (COSHH) Regulations, a carcinogen is defined as:

  • Any substance or preparation is labelled with the Risk Phrases R45 "may cause cancer" or R49 "may cause cancer by inhalation".

Carcinogens are divided into three categories:

Category 1  substances known to be carcinogenic to humans. There is sufficient evidence to establish a causal association between human exposure to the substance and the development of cancer.
Category 2  substances that should be regarded as if they are carcinogenic to humans, for which there is sufficient evidence, based on long-term animal studies and other relevant information, to provide a strong presumption that human exposure may result in the development of cancer.
Category 3  substances that cause concern owing to possible carcinogenic effects but for which available information is not adequate to make satisfactory assessments.
Categories 1 & 2 if purchased from a supplier will carry the "toxic" (T) symbol and the Risk Phrase R45 (may cause cancer) or R49 (may cause cancer by inhalation).
Category 3  if purchased from a supplier carries the "harmful" (Xn) symbol and the Risk Phrase R40 (limited evidence of carcinogenic effect).