In the general population, the causes of exposure to 4-aminobiphenyl are cigarette smoking and passive inhalation of tobacco. 4-Aminobiphenyl can occur as a contaminant in 2-aminobiphenyl, which is used in the manufacture of dyes. Other potential sources include aniline, drugs, cosmetics, color additives in food, clothes, and hair dyes. 4-Aminobiphenyl has also been found as a contaminant in diphenylamine, a fungicide used on apples, as well as in cooking oil fumes. Living near places contaminated with benzidine can lead to exposure, as certain bacteria can degrade benzidine in the environment to 4-aminobiphenyl. There are likely other sources of environmental exposure, as biomarkers derived from aromatic amines, such as hemoglobin adducts or metabolites in urine, have also been identified in nonsmokers not occupationally exposed to these chemicals. 4-Aminobiphenyl causes bladder cancer and is carcinogenic to humans. Its urinary metabolites are N-hydroxy-4-aminobiphenyl, N-glucuronides, and 4-aminobiphenyl-DNA adducts.