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What is a hazardous substance?

What is a hazardous substance?


Hazardous substances include:

  • Most hazardous chemicals (including waste and by-products)
  • Biological agents (bacteria, viruses and other micro-organisms)
  • Germs that cause diseases
  • Fumes
  • Vapours
  • Mists
  • Gases
  • Nanotechnology
  • Dust

As an employer, you have a legal responsibility to prevent employees' exposure to hazardous substances.

What law applies?

  • The Control of Substances Hazardous to Health Regulations 2002 (as amended)
  • The Control of Substances Hazardous to Health Regulations (Northern Ireland) 2003 (as amended)

(Both are known as the COSHH regulations.)

What are harmful substances?

Harmful substances include the vast majority of commercial chemicals, many of which have a hazard-warning label. Examples may include products or chemicals used for:

  • Cleaning, e.g. bleach and other cleaning agents with a warning label (not including household washing-up liquid)
  • Building maintenance, e.g. wood dust, glues and adhesives, solvents, paints and oils
  • Grounds maintenance/gardening, e.g. pesticides and chemical fertiliser
  • Healthcare, e.g. medicines and biological agents (unless patients are receiving medicine as part of their treatment)
  • Transport, e.g. oils and fuels
  • Office work/printing, e.g. printer/photocopier toner, inks and paper dust

Other hazardous substances, such as Asbestos and lead, are covered by other legislation.

The substances can be breathed in, absorbed through the skin or swallowed. The effects may be easily seen as its effects on health may develop quickly. Sometimes, effects may take years to appear, making it difficult to link the ill health to the exposure. Exposure to substances can cause skin conditions, asthma, loss of consciousness, infection and even cancer.


Under the COSSH regulations, COVID-19 is a hazardous substance if a worker comes into contact with it either:

  • by directly working with the virus, for example researching it in laboratories; or
  • due to their work activity, such as care workers caring for infectious patients.

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