A carcinogen is defined as any substance that can cause or aggravate cancer.
The International Agency for Research on Cancer assigns carcinogens a rating by grouping them into one the following five standard classifications:
- Group 1: The agent is carcinogenic to humans.
- Group 2A: The agent is probably carcinogenic to humans.
- Group 2B: The agent is possibly carcinogenic to humans.
- Group 3: The agent is not classifiable as to its carcinogenicity to humans.
- Group 4: The agent is probably not carcinogenic to humans.