Why is formaldehyde considered a significant environmental health risk despite its presence at low concentrations in outdoor air?

Formaldehyde is ubiquitously present in the ambient environment due to both natural and anthropogenic sources. Although concentrations are often low, formaldehyde is classified as a human carcinogen and contributes to both cancer and non-cancer health risks, especially under certain climatic conditions such as high temperature and solar radiation.

Formaldehyde is a significant environmental health risk because it is classified as a Group 1 human carcinogen by the IARC and is identified by the USEPA as one of the most critical hazardous air pollutants. Even low concentrations (e.g., 1 μg/m³) may elevate the risk of lung and nasopharyngeal cancers. Formaldehyde can also cause eye and respiratory tract irritation, nausea, fatigue, and in high exposures, serious conditions like emphysema and renal failure. Its health impact is exacerbated in warmer seasons due to increased photochemical formation from volatile organic compounds.