What is the IARC classification of PAHs?

Understanding IARC’s Classification of PAHs

Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals formed during the incomplete burning of organic materials like coal, oil, gas, wood, or even tobacco and charred food. Given their widespread presence in the environment, the International Agency for Research on Cancer (IARC) has evaluated several PAHs for their potential to cause cancer in humans.

The IARC classifies substances based on the strength of scientific evidence linking them to cancer. For PAHs, this classification varies. Benzo[a]pyrene (BaP), one of the most studied PAHs, is placed in Group 1: Carcinogenic to humans. This means there is sufficient evidence that BaP can cause cancer in humans, particularly through prolonged exposure via air pollution, smoking, or diet.

Other PAHs fall into Group 2A (probably carcinogenic to humans) or Group 2B (possibly carcinogenic to humans), depending on the compound and the data available. These classifications reflect differences in potency and the quality of epidemiological and experimental studies.

Interestingly, naphthalene (NaP) is also classified by IARC as carcinogenic, yet it’s often excluded from routine risk assessments. This is partly due to uncertainties in extrapolating animal data to humans and its relatively lower potency compared to BaP. Still, its presence in urban air and indoor environments—especially from sources like mothballs or cigarette smoke—keeps it on the radar of public health researchers.

Overall, while not all PAHs carry the same risk, the IARC’s tiered classification helps guide regulatory policies and risk management strategies. Limiting exposure to high-potency PAHs like BaP remains a key public health goal, especially in industrial settings and polluted urban areas.