Benzo[a]pyrene (BaP or B[a]P) is a polycyclic aromatic hydrocarbon and the result of incomplete combustion of organic matter at temperatures between 300 °C (572 °F) and 600 °C (1,112 °F).

Its diol epoxide metabolites, more commonly known as BPDE, react with and bind to DNA, resulting in mutations and eventually cancer.

A 2001 National Cancer Institute study found levels of BaP to be significantly higher in foods that were cooked well-done on the barbecue, particularly steaks, chicken with skin, and hamburgers: Cooked meat products have been shown to contain up to 4 ng/g of BaP,[5] and up to 5.5 ng/g in fried chicken[6] and 62.6 ng/g in overcooked charcoal barbecued beef.

In 1933, BaP was determined to be the compound responsible for these cases, and its carcinogenicity was demonstrated when skin tumors occurred in laboratory animals repeatedly painted with coal tar.

Pregnant rats eating BaP were shown to negatively affect the brain function in the late life of their offspring.

[13] BaP has an effect on the number of white blood cells, inhibiting some of them from differentiating into macrophages, the body's first line of defense to fight infections.

Chemical agents and related occupations, Volume 10, A review of Human Carcinogens, IARC Monographs, Lyon France 2009 [16] In June 2016, BaP was added as benzo[def]chrysene to the REACH Candidate List of Substances of very high concern for Authorisation.

[25][better source needed] Properly speaking, BaP is a procarcinogen, meaning that its mechanism of carcinogenesis depends on its enzymatic metabolism to BaP diol epoxide[27] It intercalates in DNA, and the electrophilic epoxide is attacked by nucleophilic guanine bases, forming a bulky guanine adduct.

Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide is the carcinogenic product of three enzymatic reactions:[31] BaP induces cytochrome P450 1A1 (CYP1A1) by binding to the AHR (aryl hydrocarbon receptor) in the cytosol.

Seemingly, CYP1A1 activity in the intestinal mucosa prevents major amounts of ingested benzo[a]pyrene to enter portal blood and systemic circulation.