carcinogen carcinogen a carcinogen /kɑːrsɪnədʒən/ is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). this may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. several radioactive substances are considered carcinogens, but their carcinogenic activity is attributed to the radiation, for example gamma rays and alpha particles, which they emit. common examples of non-radioactive carcinogens are inhaled asbestos, certain dioxins, and tobacco smoke. although the public generally associates carcinogenicity with synthetic chemicals, it is equally likely to arise from both natural and synthetic substances. carcinogens are not necessarily immediately toxic; thus, their effect can be insidious. cigarettes have been known carcinogens for at least 65 years. carcinogens, as mentioned, are agents in the environment capable of contributing to cancer growth. carcinogens can be categorized into two different types: activation-dependent and activation-independent, and each nature impacts their level and type of influence when it comes to promoting cancer growth. activation-dependent carcinogens require metabolic activation or modification to induce cancer, while activation-independents ones do not. examples of activation-dependent carcinogens range from certain viruses, such as hpv, to consumed alcohol, to excessive amounts of red and processed meats, impacting a person's health in ways they may not immediately associate with cancer. activation-independent carcinogens, such as ultraviolet rays or nitrosamines in tobacco products, possess characteristics enabling them to interact directly with dna and other cellular components to cause harm. these include not requiring metabolic action or molecular changes to act, which complements their ability to be electrically excited, permitting them to interact with oxygen and nitrogen atoms in negatively charged cellular environments. this type of interaction leads to the alteration of dna nucleotide bases, causing disarrangement of that genetic material. this disarrangement is also responsible for the formation of dna adducts, segments of dna which bind to carcinogens, which furthers harm. eventually, failure in dna repair mechanisms will lead to a buildup of dna damage and potentially the development of cancer. cancer is any disease in which normal cells are damaged and do not undergo programmed cell death as fast as they divide via mitosis. carcinogens may increase the risk of cancer by altering cellular metabolism or damaging dna directly in cells, which interferes with biological processes, and induces the uncontrolled, malignant division, ultimately leading to the formation of tumors. usually, severe dna damage leads to programmed cell death, but if the programmed cell death pathway is damaged, then the cell cannot prevent itself from becoming a cancer cell. there are many natural carcinogens. aflatoxin b1, which is produced by the fungus aspergillus flavus growing on stored grains, nuts and peanut butter, is an example of a potent, naturally occurring microbial carcinogen. certain viruses such as hepatitis b and human papilloma virus have been found to cause cancer in humans. the first one shown to cause cancer in animals is rous sarcoma virus, discovered in 1910 by peyton rous. other infectious organisms which cause cancer in humans include some bacteria (e.g. helicobacter pylori ) and helminths (e.g. opisthorchis viverrini and clonorchis sinensis). dioxins and dioxin-like compounds, benzene, kepone, edb, and asbestos have all been classified as carcinogenic. as far back as the 1930s, industrial smoke and tobacco smoke were identified as sources of dozens of carcinogens, including benzopyrene, tobacco-specific nitrosamines such as nitrosonornicotine, and reactive aldehydes such as formaldehyde, which is also a hazard in embalming and making plastics. vinyl chloride, from which pvc is manufactured, is a carcinogen and thus a hazard in pvc production. co-carcinogens are chemicals that do not necessarily cause cancer on their own but promote the activity of other carcinogens in causing cancer. after the carcinogen enters the body, the body makes an attempt to eliminate it through a process called biotransformation. the purpose of these reactions is to make the carcinogen more water-soluble so that it can be removed from the body. however, in some cases, these reactions can also convert a less toxic carcinogen into a more toxic carcinogen. dna is nucleophilic; therefore, soluble carbon electrophiles are carcinogenic, because dna attacks them. for example, some alkenes are toxicated by human enzymes to produce an electrophilic epoxide. dna attacks the epoxide, and is bound permanently to it. this is the mechanism behind the carcinogenicity of benzopyrene in tobacco smoke, other aromatics, aflatoxin and mustard gas. iupac definition carcinogenicity: ability or tendency to produce cancer. note: in general, polymers are not known as carcinogens or mutagens,however, residual monomers or additives can cause genetic mutations. radiation main article: radiation-induced cancer cercla identifies all radionuclides as carcinogens, although the nature of the emitted radiation (alpha, beta, gamma, or neutron and the radioactive strength), its consequent capacity to cause ionization in tissues, and the magnitude of radiation exposure, determine the potential hazard. carcinogenicity of radiation depends on the type of radiation, type of exposure, and penetration. for example, alpha radiation has low penetration and is not a hazard outside the body, but emitters are carcinogenic when inhaled or ingested. for example, thorotrast, a (incidentally radioactive) suspension previously used as a contrast medium in x-ray diagnostics, is a potent human carcinogen known because of its retention within various organs and persistent emission of alpha particles. low-level ionizing radiation may induce irreparable dna damage (leading to replicational and transcriptional errors needed for neoplasia or may trigger viral interactions) leading to pre-mature aging and cancer. not all types of electromagnetic radiation are carcinogenic. low-energy waves on the electromagnetic spectrum including radio waves, microwaves, infrared radiation and visible light are thought not to be, because they have insufficient energy to break chemical bonds. evidence for carcinogenic effects of non-ionizing radiation is generally inconclusive, though there are some documented cases of radar technicians with prolonged high exposure experiencing significantly higher cancer incidence. higher-energy radiation, including ultraviolet radiation (present in sunlight), x-rays, and gamma radiation, generally is carcinogenic, if received in sufficient doses. for most people, ultraviolet radiations from sunlight is the most common cause of skin cancer. in australia, where people with pale skin are often exposed to strong sunlight, melanoma is the most common cancer diagnosed in people aged 15–44 years. substances or foods irradiated with electrons or electromagnetic radiation (such as microwave, x-ray or gamma) are not carcinogenic. in contrast, non-electromagnetic neutron radiation produced inside nuclear reactors can produce secondary radiation through nuclear transmutation. in prepared food