What is a carcinogen?

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


Below is a list of situations where there is a proven cancer risk:

  • People smoking tobacco
  • People who previously smoked tobacco
  • Using smokeless tobacco
  • Tanning through sunlamps and solaria
  • Local atmospheric pollution from point sources of industrial emissions
  • General outdoor air pollution
  • Treatment with certain therapeutic drugs
  • Drinking alcoholic beverages
  • Occupational cancer attributable to specific agents
  • Deliberate exposure to sunlight
  • Particular work environments or job classifications
  • Residing near point sources of recognised carcinogens causing extreme local pollution
  • Passive smoking
  • Drinking water contamination from industrial sources of arsenic
  • Residential exposure to rad
    People smoking tobacco
    Situation People smoking tobacco
    Exposure Active smokers
    Carcinogen Tobacco smoke, being a mixture containing polycytic aromatic hydrocarbons and the nitrosated derivatives of nicotine and nor-nicotine.
    Principal route of exposure Inhalation
    Target organ (or tumour type) Lung, oral cavity, naso-oro & hypopharynx, nasal cavity & paranasal sinuses, larynx, stomach, esophagus, pancreas, liver, kidney, ureter, urinary bladder, uterine cervix & bone marrow
    Comment Major preventable cause of malignant disease

     

    People who previously smoked tobacco
    Situation People who previously smoked tobacco
    Exposure Ex-smokers
    Carcinogen Tobacco smoke, being a mixture containing polycytic aromatic hydrocarbons and the nitrosated derivatives of nicotine and nor-nicotine.
    Principal route of exposure Previous inhalation
    Target organ (or tumour type) Lung, oral cavity, naso-oro & hypopharynx, nasal cavity & paranasal sinuses, larynx, stomach, esophagus, pancreas, liver, kidney, ureter, urinary bladder, uterine cervix & bone marrow
    Comment Risk is reduced by comparison with continued smoking

     

    Using smokeless tobacco
    Situation Using smokeless tobacco
    Exposure Users of snuff, chewing tobacco and snus
    Carcinogen Tobacco-related nitrosamines
    Principal route of exposure Oral
    Target organ (or tumour type) Oral cavity, pancreas
    Comment Animal data establish role of nitrosamines

     

    Tanning through sunlamps and solaria
    Situation Tanning through sunlamps and solaria
    Exposure Persons using the appliances
    Carcinogen
    Ultraviolet radiation
    Principal route of exposure Irradiation
    Target organ (or tumour type) Skin
    Comment Sunlamp data plus carcinogenic hazard established in relation to solar irradiation

     

    Local atmospheric pollution from point sources of industrial emissions
    Situation Local atmospheric pollution from point sources of industrial emissions
    Exposure Residents of particular local communities
    Carcinogen
    Multiple, often unspecified, and including particulate matter, from petrochemical, steel and other industry, mainly involving sites in Europe and the United States.
    Principal route of exposure Inhalation
    Target organ (or tumour type) Lung, bladder (limited evidence)
    Comment Increased risk of lung cancer was consistently observed in cohort and case control studies. Evidence is limited in relation to bladder cancer as most studies have been of employees with potentially high exposure to outdoor air pollution rather than residents.

     

    General outdoor air pollution
    Situation
    Whole population
    Exposure Worst for residents exposed to high traffic corridors with heavy diesel emissions
    Carcinogen
    Pollutants include
    – Diesel exhaust
    – Polycyclic aromatic hydrocarbons
    – Benzene
    – Formaldehyde
    – Particulate matter
    Principal route of exposure Inhalation
    Target organ (or tumour type) Lung, bladder (limited evidence)
    Comment Evidence is limited in relation to bladder cancer as most studies have been of employees with potentially high exposure to outdoor air pollution rather than residents. Air quality monitoring and quantitative assessment is required to adequately characterise risk in differing locations.

     

    Treatment with certain therapeutic drugs
    Situation Treatment with certain therapeutic drugs
    Exposure Patients receiving relevant drugs/treatments
    Carcinogen
    Phenacetin-containing analgesics
    Diethylstilboestrol
    Cyclophosphamide & other cytotoxic drugs (including combinations)
    Combined estrogen-progestogen contraceptives
    Principal route of exposure Therapeutic administration
    Target organ (or tumour type) Target organ/tumor types specific for particular drug and include leukaemia and cancers of breast, liver, kidney and multiple other sites
    Comment Listed agents exemplify, but do not include all therapeutic drugs in the highest IARC/NTP category. Risk-benefit consideration are relevant; some drugs listed are used because of clear benefit despite a recognized hazard

     

    Drinking alcoholic beverages
    Situation Drinking alcoholic beverages
    Exposure Consumers of alcoholic beverages, and particularly those who smoke.
    Carcinogen Alcoholic beverages; (no class of drink is more markedly implicated than others)
    Principal route of exposure Oral
    Target organ (or tumour type) Oral cavity, esophagus, liver, breast
    Comment No particular category of beverage (beer, wine or spirits) is most strongly implicated.

     

    Occupational cancer attributable to specific agents
    Situation Occupational cancer attributable to specific agents
    Exposure Workers handling, or having contact with, particular chemicals or radiation
    Carcinogen
    Soot and tar
    Benzo[a]pyrene
    Asbestos
    Vinyl chloride
    Ionizing radiation Radon
    Benzene
    Cr VI , Ni, As & Cd compounds
    TCDD
    Formaldehyde
    Principal route of exposure Dermal, inhalation
    Target organ (or tumour type) Target organ depends on the agent: most commonly lung, urinary bladder and skin; all sites combined for TCDD
    Comment Agents listed are only a subset of known occupational carcinogens. Agents listed are implicated in a non-occupational environmental context addressed in Inferred risks.

     

    Deliberate exposure to sunlight
    Situation Deliberate exposure to sunlight
    Exposure White skinned populations
    Carcinogen Solar radiation; broad spectrum ultraviolet radiation
    Principal route of exposure Irradiation
    Target organ (or tumour type) Skin (cutaneous melanoma, squamous cell carcinoma, basal call carcinoma)
    Comment Account must also be taken of the beneficial effects of sunlight in relation to vitamin D.

     

    Particular work environments or job classifications
    Situation Particular work environments or job classifications
    Exposure Workers eg. work as a painter and work in the rubber industry; environments associated with aluminium production, coke production, furniture & cabinet making; iron & steel founding
    Carcinogen Some chemicals implicated (eg exposure to polycyclic aromatic hydrocarbons or aromatic amines) but causality not established because of complex exposures.
    Principal route of exposure Inhalation, and in some instances, dermal
    Target organ (or tumour type) Lung and other sites
    Comment By comparison with occupational cancers caused by particular agents, specific causative agents have not been identified in relation to the work environments listed.

     

    Residing near point sources of recognised carcinogens causing extreme local pollution
    Situation Residing near point sources of recognised carcinogens causing extreme local pollution
    Exposure Relevant local populations
    Carcinogen
    Asbestos
    Coke oven and iron foundry emissions
    Arsenic, cadmium and nickels compounds
    Principal route of exposure Inhalation in all cases
    Target organ (or tumour type) Lung and other sites depending on pollutant
    Comment Studies indicate increased cancer risk in local populations, though some studies fail to establish carcinogenic risk in this context.

     

    Passive smoking
    Situation People smoking tobacco
    Exposure Children & adults in smoker household; persons exposed as a consequence of smoking in the workplace and other environments
    Carcinogen Tobacco smoke passively inhaled
    Principal route of exposure Inhalation
    Target organ (or tumour type) Lung. Some evidence regarding larynx and other sites
    Comment Some inferences in relation to target organs apart from lung (eg. larynx)

     

    Drinking water contamination from industrial sources of arsenic
    Situation Drinking water contamination from industrial sources of arsenic
    Exposure Surrounding communities
    Carcinogen Arsenic compounds
    Principal route of exposure Ingestion
    Target organ (or tumour type) Urinary bladder & others
    Comment Many relevant studies do not established increased incidence of cancer despite clear evidence of relevant exposure.

     

    Residential exposure to radon
    Situation Residential exposure to radon
    Exposure Occupants of particular houses
    Carcinogen Radon
    Principal route of exposure Inhalation and irradiation (Yes: studies involving home exposure indicate causality)
    Target organ (or tumour type) Lung
    Comment Carcinogenic hazard established primarily by occupational studies but residential risk is specifically recognised.