by Dr Aftab Jan
Cancer is not a sudden disease. It is the final outcome of a long biological process that unfolds silently inside the body. Normal cells divide in a controlled manner. Their DNA carries instructions for growth, repair, and death. When DNA is repeatedly damaged and the repair systems fail, cells escape control. They begin uncontrolled division. Over years, these abnormal cells form tumours. Modern science clearly shows that this damage is not random in most cases. It is strongly linked to long-term exposure to specific external agents.
The International Agency for Research on Cancer operates under the World Health Organization. It is the most trusted global authority on cancer causes. Its job is scientific evaluation, not regulation. It does not approve or ban products. It reviews global evidence and classifies agents based on how strong the evidence is that they cause cancer. IARC relies on three pillars. Human epidemiological studies. Animal experimental studies. Mechanistic studies that explain how cancer develops at the cellular level. Only when evidence from these areas aligns does IARC make a strong classification.
A carcinogen is any agent that increases the risk of cancer by causing genetic mutations, chronic inflammation, hormonal imbalance, or disruption of cell regulation. Carcinogens act slowly. A single exposure rarely causes cancer. Repeated exposure over years overwhelms the body’s defenses. This explains why lifestyle and environment matter more than chance.
IARC places agents into five groups. Group 1 means carcinogenic to humans with sufficient evidence. Group 2A means probably carcinogenic with strong animal evidence and limited human data. Group 2B means possibly carcinogenic with weaker evidence. Group 3 means not classifiable due to lack of data. Group 4 means probably not carcinogenic. These groups describe certainty of evidence, not intensity of risk. Tobacco is the strongest and most preventable cause of cancer worldwide. Cigarette smoke contains more than seventy confirmed carcinogens. These include benzene, nitrosamines, formaldehyde, and polycyclic aromatic hydrocarbons. These chemicals bind directly to DNA and create mutations.
Tobacco causes lung cancer, oral cancer, throat cancer, esophageal cancer, bladder cancer, pancreatic cancer, and several others. Smokeless tobacco and pan masala are equally dangerous. They cause chronic irritation, fibrosis, and genetic damage in oral tissues. Areca nut or supari is a major cause of oral cancer in South Asia. Its active compounds trigger inflammation and precancerous lesions.
Alcohol is another Group 1 carcinogen. Inside the body, alcohol converts into acetaldehyde. This compound damages DNA and interferes with folate metabolism. Alcohol also alters oestrogen levels. This explains its strong link with breast cancer. Alcohol increases the risk of liver cancer, mouth cancer, throat cancer, and colorectal cancer. From a cancer perspective, there is no completely safe level of alcohol consumption. Processed meat is classified as Group 1. Bacon, sausages, ham, and salami contain nitrates and nitrites added for preservation. Inside the digestive system, these convert into N nitroso compounds. These compounds damage the lining of the colon and promote tumour formation. Strong evidence links processed meat to colorectal cancer.
Asbestos exposure is firmly linked to lung cancer and mesothelioma. Asbestos fibers remain lodged in lung tissue for decades. They cause chronic inflammation and genetic damage long after exposure has ended. Diesel engine exhaust and outdoor air pollution are also Group 1 carcinogens. Fine particulate matter penetrates deep into the lungs, generates oxidative stress, and damages DNA. This explains rising lung cancer rates even among non-smokers.
Ultraviolet radiation from sunlight causes direct mutations in skin cell DNA. This leads to melanoma and other skin cancers. Ionizing radiation such as X rays and gamma rays causes breaks in DNA strands. Repeated or unnecessary exposure increases leukaemia and thyroid cancer risk. Arsenic in drinking water causes skin cancer, bladder cancer, and lung cancer. Benzene damages bone marrow stem cells and causes leukemia. Formaldehyde causes nasopharyngeal cancer. Aflatoxins produced by fungi in improperly stored grains and nuts cause liver cancer by directly mutating key genes.
Infections also play a major role in cancer development. Human papillomavirus alters cell cycle control and causes cervical cancer and other genital cancers. Hepatitis B and C viruses cause chronic liver inflammation leading to liver cancer. Helicobacter pylori causes long term stomach inflammation and increases gastric cancer risk.
Red meat is classified as probably carcinogenic. Frequent consumption increases colorectal cancer risk. Heme iron in red meat promotes oxidative stress and formation of carcinogenic compounds during digestion. Very hot beverages consumed above sixty five degrees Celsius damage the lining of the esophagus. Repeated injury increases cancer risk.
Night shift work disrupts circadian rhythm. This alters melatonin secretion, immune function, and hormone regulation. Long term night work increases breast cancer risk. Certain pesticides such as glyphosate show strong animal evidence and biological mechanisms linked to cancer. Occupational exposure among hairdressers involves repeated contact with dyes and solvents. This increases bladder cancer risk. High temperature frying releases toxic fumes that damage lung tissue over time.
Nitrofurazone belongs to this group. It is an antibacterial drug previously used in veterinary medicine. Animal studies show tumor development. No safe exposure level could be established. This is why many countries banned its use in food producing animals. Mobile phone radiofrequency radiation is also classified as Group 2B. Evidence is limited but suggests a possible link to brain tumors with heavy long term use.
Traditional pickled vegetables may contain nitrosamines formed during fermentation. Lead compounds interfere with DNA repair and cell signalling. Talc contaminated with asbestos has been linked to ovarian cancer. Artificial sweetener aspartame remains under scientific evaluation with limited evidence. Group 3 includes substances for which evidence is inadequate. This does not mean safe or unsafe. It means science has not established a clear link. Tea, coffee, caffeine, fluoride, and cholesterol fall in this group. Recent studies suggest coffee may reduce liver and endometrial cancer risk.
Cancer risk depends on dose, duration, and frequency of exposure. A single exposure rarely causes cancer. Continuous exposure over years overwhelms repair systems. This explains why habits matter more than isolated events.
According to World Health Organization data, more than forty percent of cancers are preventable. Avoiding tobacco alone prevents about thirty percent of cancers. Limiting alcohol intake reduces breast and liver cancer risk. Reducing processed meat lowers colorectal cancer risk. Avoiding burnt food reduces exposure to harmful compounds. Using clean water prevents arsenic exposure. Reducing air pollution exposure protects lung health. Protecting skin from excessive sunlight prevents skin cancer. Maintaining regular sleep patterns supports hormonal balance.
Cancer is not always destiny. In many cases, it is the biological result of preventable exposure repeated over time. IARC classifications provide clarity based on evidence. When you reduce proven risks, you reduce cancer burden. Science offers knowledge. Informed choices turn knowledge into protection.
The author can be mailed at jaanaftaab5@gmail.com
