Cancer is developed from a damaged cell. Our body’s normal functions are controlled by all kinds of cells, once these cells are damaged; abnormal cells’ behaviors emerged, causing tumors. Tumors can be classified into benign and malignant, malignant tumors are what we called “cancer”. Anything that triggers the damages of cells is the causative factors of cancers.

There are many possible reasons for gene mutations. Except hereditary factors, exposure to carcinogens is another main reason causing gene mutation and cells damage. Carcinogens are substances which have scientifically proven to increase the chance of causing human cancers. International Agency for Research on Cancer (IARC) is an organisation under World Health Organisation (WHO), dedicated to classify substances into different groups according to their carcinogenic nature; it aims at providing a standard reference for the world. Among all, we have to pay attention to substances in group I as they are considered as carcinogenic to humans.

Group Definition
1 Carcinogenic to humans
2A Probably carcinogenic to humans
2B Possibly carcinogenic to humans
3 Not classifiable as to its carcinogenicity to humans
4 Probably not carcinogenic to humans

Group 1 carcinogens
1. Tobacco smoking (including second-hand smoking)
2. Alcoholic beverages
3. Areca nut
4. Coal, indoor emissions from household combustion of
5. Engine exhaust, diesel
6. Epstein-Barr virus
7. Estrogen-progestogen oral contraceptives (combined)
8. Helicobacter pylori (infection with)
9. Hepatitis B virus (chronic infection with)
10. Hepatitis C virus (chronic infection with)
11. Tamoxifen
12. Vinyl chloride
13. Leather dust
14. Outdoor air pollution
15. Processed meat (consumption of)
16. Salted fish, Chinese-style
17. Solar radiation
18. Tobacco smoke, second-hand
19. Wood dust

Group 2A/2B carcinogens
1. Red Meat (consumption of)
2. Malaria
3. Frying, emissions from high-temperature
4. Human papillomavirus type 68
5. Hairdresser or barber (occupational exposure)
6. Surgical implants and other foreign bodies
7. Pickled vegetables (traditional Asian)
8. Gasoline
9. Coffee (urinary bladder)
10. Coconut oil diethanolamine condensate
11. Talc-based body powder (perineal use of)
12. Lead
13. Caffeic acid

For more details, please refer to the website of IARC: