Exposure to carcinogens, mutagens and biological agents

Regulation 9 of the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR) requires employers and self-employed workers to report:

  • any disease caused by an occupational exposure to a biological agent
  • cases of occupational cancer

Reasonable evidence of occupational exposure

For an occupational exposure to be judged as the likely cause of the condition, there should be reasonable evidence that the person's work activity was the source of exposure.

Such reasonable evidence will include whether the person's work activities involved deliberate work with a known carcinogen or biological agent.

Occupational cancers

Occupational cancer is caused by significant exposure to carcinogens and mutagens in the workplace, often over a prolonged period. They can be:

  • solid substances
  • liquids
  • mixtures
  • vapours
  • gases
  • dusts
  • ionising radiation

How workers can be exposed to carcinogens

Without adequate control measures in place, a person at work can be exposed to carcinogens by:

  • breathing them in
  • absorbing them through the skin
  • accidental swallowing

These hazards cover all known human carcinogens. They also cover mutagens which are agents, such as ionising radiation or a chemical substance, that cause genetic mutation.

When cases of cancer must be reported

Cases of cancer must be reported where there is an established causal link between the type of cancer diagnosed and the hazards to which the person has been exposed through work.

For example, the following diagnosed occupational cancers must be reported:

  • mesothelioma or lung cancer in a person who is occupationally exposed to asbestos fibres
  • cancer of the nasal cavity or sinuses in a person who is occupationally exposed to wood dust

Reports are only required when the person's work significantly increases the risk of developing the cancer. In some cases, a medical practitioner may indicate the significance of any occupational factors when making the diagnosis.

When cases of cancer are not reportable

Cases of cancer are not reportable when they are not linked with work-related exposures to carcinogens or mutagens.

As with other diseases, cancers are only reportable if the person's current job involves exposure to the relevant hazard.

Biological agents

All diseases must be reported when they are attributable to an occupational exposure to a biological agent.

The term biological agent is defined in the Control of Substances Hazardous to Health Regulations (COSHH). It means a micro-organism, cell culture or human endoparasite which may cause infection, allergy, toxicity or other hazard to human health.

Work with hazardous biological agents is subject to specific provisions under COSHH.

How workers may be exposed to biological agents

Occupational exposures to biological agents may take place as a result of:

  • an identifiable event, such as accidental breakage of a laboratory flask, accidental injury with a contaminated syringe needle or an animal bite
  • unidentified events, where workers are exposed to the agent without their knowledge (for example being exposed to legionella during routine maintenance on a hot water service system)

When to report a disease

A report should be made whenever there is reasonable evidence that an occupational exposure was the likely cause of the disease.

A medical practitioner making the diagnosis may indicate the significance of any occupational factors.


Infections, such as colds, flu, bronchitis or stomach upsets, cannot usually be attributed to occupational exposures to biological agents, so are generally not reportable.

However, where there is reasonable evidence of an occupational exposure to the infection, you should make a report. An example of this is inadvertent contact with the infectious agent during laboratory work.

Other occupational diseases

There is guidance on occupational diseases that must be reported under Regulation 8 of RIDDOR when they are linked to exposure to specified hazards at work.

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Updated 2024-06-04