Carcinogens are agents that can increase the likelihood of developing cancer. Experts have identified over 100 types of carcinogens, which include physical sources like UV radiation from the sun, chemical substances such as asbestos, and biological factors, including certain virus-related infections. While exposure to a carcinogen does not automatically lead to cancer, there are steps you can take to minimize the risk associated with such exposure.
Carcinogens contribute to cancer development by interacting with the genetic makeup of cells. Understanding the relationship between carcinogens and your DNA can help explain how these substances initiate cancer. DNA within genes provides instructions for producing proteins that regulate various cell functions, including growth and division. If a carcinogen affects the DNA, it can trigger changes that convert normal cells into cancerous ones.
In some cases, carcinogens directly harm the DNA, causing errors in its function. Sometimes, the body’s natural mechanisms for repairing DNA may fail to fix the damage. If this repair process is unsuccessful, mutations can occur within the genes. Depending on the type of mutation, it may cause cells to reproduce uncontrollably, which can result in tumor formation or even blood cancers.
However, cancer does not usually develop immediately following carcinogen exposure. It may take years for carcinogen accumulation in the body to initiate the process that leads to cancer.
You may be exposed to carcinogens in several ways, such as:
- Engaging in activities like smoking.
- Working in environments that use chemicals linked to cancer.
- Carrying viruses such as human papillomavirus (HPV), which is known to cause cancer.
However, contact with a carcinogen doesn’t necessarily lead to cancer. Some factors that affect the risk include:
- Long-term exposure: For example, a person who has smoked for many years or frequently encounters secondhand smoke has a higher cancer risk compared to someone who avoids smoking or smoke exposure.
- Frequent exposure: High alcohol consumption is linked to an increased cancer risk. Health guidelines recommend no more than two drinks per day for men and one for women.
- Inherited genetic mutations: Certain cancers are hereditary, and genetic mutations passed through families can elevate cancer risk. In combination with exposure to carcinogens, this risk can be even higher.
Who determines if something is carcinogenic?
In the U.S., the National Toxicology Program (NTP) reviews research and compiles lists of known and potential carcinogens. Internationally, the International Agency for Research on Cancer (IARC) carries out similar assessments. Both organizations rely on laboratory tests and studies to determine if a substance can cause cancer.
The latest NTP report lists 63 known carcinogens and 193 other substances that may be linked to cancer. The IARC has identified 122 known carcinogens, 93 likely carcinogens, and 319 that could pose a cancer risk.
Carcinogens are classified by the International Agency for Research on Cancer (IARC) into three main categories:
- Physical carcinogens: These include UV radiation from the sun and ionizing radiation, which can come from radon gas in homes or from medical procedures such as X-rays.
- Chemical carcinogens: Examples are substances like asbestos, tobacco smoke, alcohol, aflatoxins (toxins produced by molds that can contaminate food), and arsenic, which is naturally present in the environment, including in air, water, and soil.
- Biological carcinogens: These are infections caused by certain viruses, bacteria, or parasites that can lead to cancer.
Some common carcinogens include alcoholic beverages, which the NTP identifies as a known carcinogen. Alcohol consumption is linked to an increased risk of various cancers, including:
- Oral cancer
- Pharyngeal and laryngeal cancers
- Colorectal cancer
- Esophageal cancer
- Liver cancer
- Breast cancer
- Stomach cancer
Alcohol increases cancer risk for several reasons, including:
- Acetaldehyde production: When the body breaks down alcohol (ethanol), it forms acetaldehyde, a known carcinogen. This substance damages DNA and disrupts the cell’s ability to repair itself, which can promote the growth of cancer cells.
- Hormonal effects: Alcohol can alter hormone levels, particularly estrogen. These hormones regulate cell growth and division, and an increase in cell division heightens the chance of errors that could lead to cancer.
- Reduced nutrient absorption: Alcohol interferes with the body’s ability to absorb and utilize essential vitamins and minerals such as vitamins A, B1, B6, C, D, E, K, folate, iron, and selenium. These nutrients are important for immunity, protecting cells from oxidative damage, reducing inflammation, and supporting DNA repair.
- Weight gain: Excessive alcohol consumption contributes to weight gain due to increased calorie intake. Being overweight or obese is linked to a higher risk of more than 12 different types of cancer.
- Heightened risk from tobacco: Drinking alcohol while using tobacco products increases the risk of cancers like oral and throat cancer. Alcohol makes cells more susceptible to carcinogens found in tobacco, and the combination of drinking and smoking significantly raises cancer risk compared to either habit alone.
Additionally, all forms of tobacco—whether cigarettes, cigars, pipes, shisha, or smokeless tobacco—are carcinogenic.
Does light, occasional and social smoking cause cancer?
Yes, even “light,” “occasional,” or “social smoking” increases the risk of cancer. Research shows that smoking less than one cigarette per day still raises the likelihood of early death compared to non-smokers. Studies have also found that individuals who smoke fewer than 10 cigarettes daily are at an elevated risk for smoking-related cancers and other diseases.
Cutting down on the number of cigarettes smoked is a positive first step, but no level of smoking is considered safe. The best way to protect your health is to quit smoking entirely, and it’s never too late to do so.
Ultraviolet (UV) rays from the sun or from radiation therapies can also cause skin cancer. Exposure to UV radiation, whether from sunlight or tanning devices, is a known risk factor for all skin cancer types. Those at higher risk include individuals with weakened immune systems, a personal or family history of skin cancer, and those with many or large moles.
Most skin cancers are due to UV exposure from sunlight. The most common types—basal cell and squamous cell cancers—typically develop on areas of the skin frequently exposed to the sun and are often related to cumulative lifetime sun exposure. Melanoma, while less common, is more serious and is also linked to sun exposure. In addition to natural sunlight, exposure to artificial sources of UV rays, like tanning beds, has also been associated with skin cancer.
Radon is a colorless, odorless gas that can be present in buildings like homes, schools, and workplaces. Exposure to radon is the second leading cause of lung cancer. Organizations such as the World Health Organization (WHO), the National Academy of Sciences, the U.S. Department of Health and Human Services, and the Environmental Protection Agency (EPA) classify radon as a known carcinogen. This classification is based on extensive biological and epidemiological evidence linking radon exposure to lung cancer in humans.
Asbestos was commonly used as insulation in buildings before 1989, when the U.S. Environmental Protection Agency (EPA) banned new uses of the material. People may still encounter asbestos in older buildings. Exposure to asbestos has been linked to several cancers, including malignant mesothelioma, lung cancer, laryngeal cancer, and ovarian cancer.
When asbestos fibers are inhaled or ingested, they can lodge in the tissues around the lungs or abdomen, causing long-term inflammation and cell damage. Over time, these fibers can lead to DNA damage, resulting in abnormal cell growth and cancer. Asbestos exposure is responsible for half of all occupational cancer deaths.
Formaldehyde exposure, particularly in the workplace, has been linked to an increased risk of acute myeloid leukemia as well as rare cancers in the nasal cavities and sinuses. The U.S. Environmental Protection Agency (EPA) maintains the Integrated Risk Information System (IRIS), a database that provides information on the health effects of various environmental substances. The EPA has classified formaldehyde as a human carcinogen when inhaled, citing evidence of increased risks for nasopharyngeal cancer, nasal sinus cancer, and myeloid leukemia, along with potential links to other types of cancer.
Processed meats, which are meats altered through methods like salting, curing, or smoking, have been associated with an increased risk of colorectal cancer. Research indicates that both red and processed meats contain specific chemicals—some added during processing and others that occur naturally—that can contribute to their carcinogenic properties. For instance, when the chemical haem found in red meat is metabolized in the digestive system, it produces N-nitroso compounds, which can harm the cells lining the bowel and potentially result in bowel cancer. Similarly, these harmful chemicals are also generated when processed meats are digested. Additionally, preservatives like nitrites and nitrates, commonly used in processed meats, can also lead to the formation of N-nitroso compounds, further increasing the risk of bowel cancer.
While it’s impossible to completely eliminate exposure to all carcinogens, you can take steps to minimize your risk by:
- Avoiding tobacco products.
- Limiting or abstaining from alcohol consumption.
- Getting vaccinated against cancers linked to certain viruses.
- Protecting your skin from sun exposure and other sources of ultraviolet (UV) radiation.
When should you reach out to a doctor regarding carcinogen exposure?
It’s a good idea to consult a healthcare provider if you use tobacco or frequently drink alcohol. They can recommend cessation programs or strategies for reducing your alcohol intake. Additionally, you might want to discuss your lifetime cancer risk, as detailed by the National Cancer Institute. If you have a higher risk for a specific type of cancer, it may be wise to avoid carcinogens related to that cancer.
Based on your individual health situation, your provider may also recommend certain cancer screening tests.
