Instruct: Given a question, retrieve documents that answer the question.
Query: Do polycyclic aromatic hydrocarbons cause cancer?
PAHs have been linked to skin, lung, bladder, liver, and stomach cancers in well-established animal model studies.[52] Specific compounds classified by various agencies as possible or probable human carcinogens are identified in the section "Regulation and Oversight" below.
U.S. Department of Health and Human Services NASA Spitzer Space Telescope Aromatic World An interview with Professor Pascale Ehrenfreund on PAH origin of life. Accessed June 2006 focused on new technologies and emerging health risks of Polycyclic Aromatic Hydrocarbons (PAHs) . U.S. Environmental Protection Agency, Office of Solid Waste, January 2008.
An aromatic hydrocarbon or arene (or sometimes aryl hydrocarbon) is a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle. In contrast, aliphatic hydrocarbons lack this delocalization. The term "aromatic" was assigned before the physical mechanism determining aromaticity was discovered; the term was coined as such simply because many of the compounds have a sweet or pleasant odour. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon, benzene. Aromatic hydrocarbons can be "monocyclic" (MAH) or "polycyclic" (PAH).
A spectral database exists[79] for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe.[80] Detection of PAHs in materials is often done using gas chromatography-mass spectrometry or liquid chromatography with ultraviolet-visible or fluorescence spectroscopic methods or by using rapid test PAH indicator strips.
Many of the polycyclic aromatic hydrocarbons known to be tumorigenic or mutagenic are found in atmospheric aerosols, which is connected to the thermal rearrangement of polycyclic aromatic hydrocarbons in fast soot formation during combustion.
Considered probable or possible human carcinogens by the US EPA, the European Union, and/or the International Agency for Research on Cancer (IARC).[78][1]
Other chemicals found in tobacco can also cause cancer. These include: A radioactive element (polonium-210) found in tobacco fertilizer. Chemicals formed when tobacco is cured with heat (polynuclear aromatic hydrocarbons—also known as polycyclic aromatic hydrocarbons). Harmful metals (arsenic, beryllium, cadmium, chromium, cobalt, lead, nickel, mercury). Products such as 3-(methylnitrosamino)-proprionitrile, nitrosamines, and nicotine initiate the production of reactive oxygen species in smokeless tobacco, eventually leading to fibroblast, DNA, and RNA damage with carcinogenic effects in the mouth of tobacco consumers. The metabolic activation of nitrosamine in tobacco by cytochrome P450 enzymes may lead to the formation of N-nitrosonornicotine, a major carcinogen, and micronuclei, which are an indicator of genotoxicity. These effects lead to further DNA damage and, eventually, oral cancer. Smokeless tobacco can cause white or gray patches inside the mouth (leukoplakia) that can lead to cancer. The World Health Organization has classified smokeless tobacco products as human carcinogenic compounds, in particular tobacco-specific nitrosamines, which account for 76 to 91% of the total N-nitroso compound (NOC) burden. A 2014 review found there is "a number of ethnically linked smokeless tobacco types that contain areca nut, a Group 1 carcinogen. Use of areca nut-containing smokeless tobacco is known to cause oral cancer, yet despite this, prevalence is increasing in the Western Pacific."
Priority polycyclic aromatic hydrocarbons identified by the US EPA, the US Agency for Toxic Substances and Disease Registry (ATSDR), and the European Food Safety Authority (EFSA) due to their carcinogenicity or genotoxicity and/or ability to be monitored are the following:[76][77][78]
Tobacco smoke, for example, causes 90% of lung cancer. It also causes cancer in the larynx, head, neck, stomach, bladder, kidney, esophagus and pancreas. Tobacco smoke contains over fifty known carcinogens, including nitrosamines and polycyclic aromatic hydrocarbons.
Polycyclic aromatic hydrocarbons are discussed as possible starting materials for abiotic syntheses of materials required by the earliest forms of life.
Contorted aromatics or more precisely contorted polycyclic aromatic hydrocarbons represent a unique class of polycyclic aromatic hydrocarbons (PAHs) in which the fused aromatic molecules deviate from the usual planarity.
Polycyclic aromatic hydrocarbons (PAHs), fused-ring chemicals formed during the combustion of fossil fuels, are metabolized by the cytochrome P450 complex to highly reactive carbocations, which can mutate DNA and cause cancer. Workers may be exposed to PAHs while working in a foundry, in the roofing industry, or due to environmental tobacco smoke.
Polycyclic aromatic hydrocarbons (PAHs) are aromatic hydrocarbons that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH. PAHs occur in oil, coal, and tar deposits, and are produced as byproducts of fuel burning (whether fossil fuel or biomass). As pollutants, they are of concern because some compounds have been identified as carcinogenic, mutagenic, and teratogenic. PAHs are also found in cooked foods. Studies have shown that high levels of PAHs are found, for example, in meat cooked at high temperatures such as grilling or barbecuing, and in smoked fish.
Other risk factors include radiation and shift-work. A number of chemicals have also been linked, including polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and organic solvents Although the radiation from mammography is a low dose, it is estimated that yearly screening from 40 to 80 years of age will cause approximately 225 cases of fatal breast cancer per million women screened.
The structure of a PAH influences whether and how the individual compound is carcinogenic.[52][56] Some carcinogenic PAHs are genotoxic and induce mutations that initiate cancer; others are not genotoxic and instead affect cancer promotion or progression.[56][57]
Researchers from NCI (National Cancer Institutes) and Brazil found both cold- and hot-water extractions of popular commercial yerba mate products contained high levels (8.03 to 53.3 ng/g dry leaves) of carcinogenic polycyclic aromatic hydrocarbons (PAHs) (i.e. benzo[a]pyrene). However, these potential carcinogenic compounds originated from the commercial drying process of the mate leaves, which involves smoke from the burning of wood, much like polycyclic aromatic hydrocarbons found in wood-smoked meat. "Unsmoked" or steamed varieties of yerba mate tea are also available.
Polycyclic aromatic hydrocarbons are molecules containing two or more simple aromatic rings fused together by sharing two neighboring carbon atoms (see also simple aromatic rings). Examples are naphthalene, anthracene, and phenanthrene. In fused aromatics, not all carbon–carbon bonds are necessarily equivalent, as the electrons are not delocalized over the entire molecule. The aromaticity of these molecules can be explained using their orbital picture. Like benzene and other monocyclic aromatic molecules, polycyclics have a cyclic conjugated pi system with p-orbital overlap above and below the plane of the ring.
AhR ligands have been generally classified into two categories, synthetic or naturally occurring. The first ligands to be discovered were synthetic and members of the halogenated aromatic hydrocarbons (polychlorinated dibenzodioxins, dibenzofurans and biphenyls) and polycyclic aromatic hydrocarbons (3-methylcholanthrene, benzo["a"]pyrene, benzanthracenes and benzoflavones).
Anthanthrene is a polycyclic aromatic hydrocarbon. According to the International Agency for Research on Cancer, there was "limited evidence in experimental animals" that it is a carcinogen.
Erich Clar (August 23, 1902 – March 27, 1987) was an organic chemist who studied polycyclic aromatic hydrocarbon chemistry. He is considered as the father of that field. He authored the two-volume "Polycyclic Hydrocarbons", which described the syntheses, properties, and UV-visible absorption spectra of hundreds of PAHs. He created the Sextet Theory, now eponymously called "Clar's rule", to describe the behavior of PAH isomers. This was described in his book "The Aromatic Sextet". He was awarded the August Kekulé Medal by the Chemical Society of the GDR in 1965, the highest award given by that society to foreign scientists, and the first Polycyclic Aromatic Hydrocarbon Research Award of the International Symposium on Polynuclear Aromatic Hydrocarbons in 1987.
Cancer is a primary human health risk of exposure to PAHs.[52] Exposure to PAHs has also been linked with cardiovascular disease and poor fetal development.
Thermal rearrangements of aromatic hydrocarbons are considered to be unimolecular reactions that directly involve the atoms of an aromatic ring structure and require no other reagent than heat. These reactions can be categorized in two major types: one that involves a complete and permanent skeletal reorganization (isomerization), and one in which the atoms are scrambled but no net change in the aromatic ring occurs (automerization). The general reaction schemes of the two types are illustrated in Figure 1.
This class of reactions was uncovered through studies on the automerization of naphthalene as well as the isomerization of unsubstituted azulene, to naphthalene. Research on thermal rearrangements of aromatic hydrocarbons has since been expanded to isomerizations and automerizations of benzene and polycyclic aromatic hydrocarbons.
Acenaphthylene is a polycyclic aromatic hydrocarbon. The molecule resembles naphthalene with positions 1 and 8 connected by a CH unit. It is a yellow solid. Unlike many polycyclic aromatic hydrocarbons, it has no fluorescence. 
Indenofluorenes (IFs) are members of the family of polycyclic hydrocarbons which incorporate a core Indene and a core Fluorene to form a 6-5-6-5-6 ring system. While IFs are members of the polycyclic hydrocarbon family, they are not necessarily members of the polycyclic aromatic hydrocarbon family. For example, the fully conjugated versions, shown below, have 20π electrons making them formally anti-aromatic. Depending on the way that the indene and fluorene are connected, five regioisomers can be formed where each regioisomer has unique properties, applications and extent of study. 
Stir frying is not without health risks. Recent studies show that heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are formed by stir frying meat at very high temperatures. These chemicals cause DNA changes that may contribute to increased risk of cancer.