What are carcinogens? A carcinogen, as the name suggests, is a substance that can induce cancer in humans. Broadly speaking, carcinogens should be referred to as cancer-causing factors, including any chemical, physical, or biological substances, as well as lifestyle and work practices, that increase the risk of cancer in humans. In 1965, the International Agency for Research on Cancer (IARC), a division of the World Health Organization, was established. The work of identifying carcinogens has been carried out since the organization was established. Every year, IARC publishes authoritative information to update the information of carcinogens. Eventually, IARC identified the concept of carcinogens and classified them into four categories. Interpretation of carcinogen classification: Class 1 carcinogens are substances with “clear” carcinogenic effects. The common ones in our life are tobacco, alcoholic beverages, betel nut, aflatoxin, asbestos, etc. Class 2A carcinogens are substances with “high probability” of causing cancer. It means that animal experiments have confirmed a clear carcinogenic effect, but evidence from population studies is still limited. The common ones are acrylamide, high-temperature fried food, high-temperature oil fumes, reversal of work and rest, inorganic lead compounds, etc. Group 2B carcinogens are substances that have a “low probability” of causing cancer. The evidence for the “carcinogenic potential” of these substances in animal studies and population studies is not very strong for the time being. The common ones are chloroform, fern, DDT (a pesticide), nitrobenzene, gasoline (car exhaust), and cell phone radiation (non-ionizing radiation). The third category of carcinogens is “not yet classifiable” carcinogens. There are two types of carcinogens that cannot be classified: those with insufficient evidence of carcinogenicity in animal studies and population studies, and those with sufficient evidence in animal studies but no clear carcinogenic effect in population studies. The common ones are caffeine, xylene, saccharin, Valium, static electromagnetic fields, organic lead compounds, etc. Class 4 carcinogens are substances that are “probably not” carcinogenic to humans. There is no sufficient evidence of carcinogenicity in relevant studies. Currently, there is only one “caprolactam” in the information published by IARC. How to deal with carcinogens? Class 1 and 2A carcinogens should be avoided. For Class 1 and 2A carcinogens, national public health policies are in place to reduce the exposure level of the population, and we should also try to avoid exposure to these carcinogens. Here are two examples to talk about. Tobacco is a Class 1 carcinogen Beijing implemented the so-called “toughest ever” anti-smoking regulation on June 1, 2015. In summary, smoking is banned in all public places with a “roof” and “lid”, and all forms of tobacco advertising are banned. Acrylamide is a Class 2A carcinogen. Acrylamide is closely related to bowel cancer, and is more commonly found in French fries, which contain large amounts of acrylamide. The U.S. Department of Agriculture has adopted a policy that permits the commercial cultivation of a genetically modified potato (RNAi potato), which greatly reduces the production of acrylamide during the frying process. Class 2B carcinogens are not a cause for concern. National public health policies are not yet required for Class 2B carcinogens, and personal protection is not mandatory. Typical representatives of carcinogens in category 2B are non-ionizing radiation, such as radiofrequency electromagnetic fields emitted from cell phones, computers and WiFi devices. There is not enough evidence to confirm the carcinogenic effect of non-ionizing radiation, so no country has adopted public policies to restrict its use by claiming that non-ionizing radiation can affect health. However, some authorities have given some personal recommendations for reducing exposure to electromagnetic radiation from cell phones, including reducing the time of use and using hands-free devices to take calls. It should be noted that these are only recommended advice, not mandatory. For the carcinogens in category 3 and 4, we should not be too concerned about them, because no relevant studies have found that they can cause cancer. The classification of carcinogens only tells us the level of evidence of carcinogens; the intensity of carcinogenicity is related to the characteristics of carcinogens themselves and the exposure level (dose) of carcinogens. Therefore, drinking and smoking a few times does not mean that you will get cancer. However, the risk of cancer increases significantly with prolonged and heavy drinking and smoking. If you quit smoking and drinking and avoid exposure to carcinogens, you can certainly reduce the risk of cancer.