A study published in the journal BMJ Open demonstrated that exposure to polycyclic aromatic hydrocarbons (PAH) present in the environment is strongly linked to developing rheumatoid arthritis risk.

The study enrolled 21,987 people, among which 1418 suffered from rheumatoid arthritis and 20,569 did not. The total quantity of PAH, plastics and various consumer products (PHTHTEs), and Volatile organic compounds (VOCs), in the body was determined using blood and urine samples. Those in the top 25% of body PAH levels had the highest risk of rheumatoid arthritis, regardless of whether they were previous or current smokers. Only one PAH, 1-hydroxy naphthalene, was shown to be strongly related to an increased risk of rheumatoid arthritis in this investigation.

Results from the study showed that body PAH levels were responsible for 90% of the total effect of smoking on rheumatoid arthritis risk, while VOCs, their metabolites and PHTHTEs did not contribute to the increased risk. 

This is the first study to indicate that PAH not only supports the majority of the association between smoking and rheumatoid arthritis but also is a strong independent contributor.

Adult smokers exhibited higher levels of PAHs, but other sources of PAH exposure, such as the environment of indoor setups, exhaust from the motor vehicle, natural gas, asphalt road emissions, smoke from wood or coal-burning fires, and consuming grilled or charred foods, also increased the risk. 

People with low socioeconomic status are also particularly vulnerable as they reside in urban areas next to major roadways or in high-traffic areas and are continuously exposed to poorer indoor air quality.

(Source: https://www.news-medical.net/news/20230510/Environmental-PAH-exposure-associated-with-increased-rheumatoid-arthritis-risk.aspx)