Smoking is an important risk factor for RA; and nicotine exerts effects via Th17 cells; Aryl-hydrocarbon Receptor (AhR) binding by aromatic hydrocarbons and non-halogenated polycyclic aromatic hydrocarbons favors differentiation of Th17 cells and can exacerbate autoimmunity. Here, AHR is linked to rheumatoid arthritis.