Polycyclic Aromatic Hydrocarbons (PAHs) Factsheet

Polycyclic aromatic hydrocarbons (PAHs) are a class of chemicals that occur naturally in coal, crude oil, and gasoline. They result from burning coal, oil, gas, wood, garbage, and tobacco. PAHs can bind to or form small particles in the air. High heat when cooking meat and other foods will form PAHs. Naphthalene is a manmade PAH used in the United States to make other chemicals and mothballs. Cigarette smoke contains many PAHs.

PAH Exposure in People

Exposure to PAHs can occur by:

  • Breathing air containing
    • Motor vehicle exhaust
    • Cigarette smoke
    • Wood smoke
    • Fumes from asphalt roads
  • Consuming grilled or charred meats or foods
  • Eating foods on which PAH particles have settled from the air
  • In some cases, passing through the skin.

After PAHs enter a person, the body converts PAHs into breakdown products called metabolites. The metabolites pass out of the body in the urine and feces.

How PAHs Affect People’s Health

Human health effects from indirect exposure to low levels of PAHs are unknown. Large amounts of naphthalene in air can irritate eyes and breathing passages. Occupational skin exposure with liquid naphthalene and breathing its vapors may be harmful. Workers have become sick with blood and liver problems from large amounts of exposure. Scientists consider several of the PAHs and some specific mixtures to be cancer-causing chemicals.

Levels of PAH Metabolites in the U.S. Population

CDC scientists measured ten different PAH metabolites in the urine of 2,504 or more participants aged six years and older. These were individuals who took part in the National Health and Nutrition Examination Survey (NHANES) during 2003–2004. By measuring PAH metabolites in urine, scientists can estimate the amounts of PAHs that have entered people’s bodies.

Scientists found PAHs in most of the study’s participants, showing widespread exposure in people in the U.S. Research has found that PAH metabolites in urine are higher in adults who smoke than in nonsmoking adults. The data tables showing results are available here: https://www.cdc.gov/exposurereport/.

Finding one or more PAH metabolites in the urine does not imply that these levels cause an adverse health effect. By measuring levels of PAH metabolites in people, scientists can give health officials a basis for comparing results in a society. They can see whether people have higher levels of PAH metabolites in their bodies than normal.

By measuring chemicals in the body, scientists also can plan and conduct research on exposure and health effects.

Additional Resources

Agency for Toxic Substances and Disease Registry

Page last reviewed: March 2, 2022