How carcinogenic chemicals are classified and tracked globally

Why carcinogen classification matters

Accurate classification is the foundation of global chemical safety. It ensures that manufacturers, suppliers, and consumers understand the cancer-related hazards of specific substances and can take appropriate measures — from safe handling and labelling to substitution and regulatory compliance. 

For compliance teams, classification frameworks also serve as the basis for restrictions, authorizations, and reporting obligations under key chemical regulations such as REACH in the EU, Proposition 65 in California, and similar frameworks adopted worldwide. 

The three most widely used global frameworks for classifying carcinogens are IARC, GHS/CLP, and the EU’s REACH Regulation.

International Agency for Research on Cancer (IARC) carcinogen classifications

The International Agency for Research on Cancer (IARC), part of the World Health Organization, is the most widely recognized authority for assessing the carcinogenicity of substances. IARC reviews scientific evidence from human and animal studies and assigns substances to one of four groups: 

Note: IARC groups reflect the strength of evidence that an agent can cause cancer (hazard), not the level of risk at a specific exposure. 

Group 1 – Carcinogenic to humans

Sufficient evidence from human studies; examples include asbestos, benzene, and formaldehyde.

Group 2A – Probably carcinogenic to humans

Used when there is limited evidence of carcinogenicity in humans and either:

• sufficient evidence of carcinogenicity in experimental animals, or
• strong mechanistic evidence showing that the agent exhibits key characteristics of human carcinogens.

Group 2B – Possibly carcinogenic to humans

Used when the evidence of carcinogenicity is more limited, typically when only one of the following is available:

• limited evidence in humans, or
• sufficient evidence in experimental animals, or
• strong mechanistic evidence showing key characteristics of human carcinogens.

Group 3 – Not classifiable as to carcinogenicity in humans

Inadequate evidence of carcinogenicity in humans or limited evidence of carcinogenicity in experimental animals, and mechanistic evidence is limited. 

In practice, IARC classifications are used by regulators, scientists, and industry professionals worldwide to support policy decisions, hazard communication, and risk assessments. 

Globally Harmonized System (GHS/CLP) carcinogen categories

The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) provides a common international language for identifying chemical hazards — including carcinogenicity. 

Under GHS, carcinogens are assigned to three hazard categories: 

Category 1A – Known human carcinogens

Largely based on human evidence 

Category 1B – Presumed human carcinogens

Largely based on animal evidence

Category 2 – Suspected human carcinogens

In the European Union, GHS is implemented through the Classification, Labelling and Packaging (CLP) Regulation. Substances meeting these criteria must include appropriate hazard statements (e.g., H350: May cause cancer), pictograms, and safety information on labels and Safety Data Sheets (SDSs). 

EU REACH Regulation: carcinogens and SVHCs

The EU’s REACH Regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals) builds on GHS classifications to control hazardous substances on the market. 

Substances of Very High Concern (SVHCs)

Carcinogens meeting certain criteria are added to the Candidate List, which triggers communication duties and potential consumer disclosure requirements. 

Annex XIV – Authorisation List

SVHCs listed here cannot be used or placed on the market without authorization or exemption for specific use. 

Annex XVII – Restrictions List

Limits or bans the marketing and use of certain hazardous substances, mixtures, and articles including certain known carcinogens. 

These lists are regularly updated as new scientific evidence emerges — meaning companies must monitor changes and adapt formulations, labelling, and supplier documentation accordingly. 

Global context and other frameworks

While IARC, GHS, and REACH are the primary international systems, many other jurisdictions have adopted similar approaches. 

United States

• Occupational Safety and Health Administration (OSHA) applies hazard communication standards aligned with GHS. 
• California Proposition 65 mandates warnings for products containing substances known to cause cancer. 
• National Toxicology Program (NTP) Report on Carcinogens is a science-based public health document that includes listings of chemical, physical, and biological agents; mixtures, and exposure circumstances that are known or reasonably anticipated to cause cancer in humans. 

Asia-Pacific

• China, Japan, and South Korea have national GHS-based systems that classify carcinogens and restrict their use in consumer and industrial products. 

Other regions

• Canada’s WHMIS 2015 and Australia’s Work Health and Safety (WHS) Regulations are also aligned with GHS principles. 

Together, these frameworks create a global network of carcinogen management that drives transparency and consistency in chemical safety worldwide. 

What this means for businesses

For manufacturers, importers, and downstream users, carcinogen classification is not just a regulatory exercise — it’s a cornerstone of chemical risk management. Because classifications drive restrictions, warnings, and reporting obligations across jurisdictions, ongoing monitoring is essential.

Companies must: 

• Track which substances in their products fall under IARC, GHS, or REACH carcinogenicity classifications. 

• Update Safety Data Sheets and labels accordingly. 

• Communicate classification information throughout the supply chain. 

• Screen substances early to avoid compliance breaches and costly reformulations. 

Centralizing this process with regulatory intelligence tools can simplify compliance and improve visibility across global operations.