Like other autoimmune diseases, including adult RA, risk of developing juvenile idiopathic arthritis (JIA) is thought to be determined by a complex combination of genetic and environmental factors.

Although some predisposing JIA genes are now being identified, research aimed at identifying environmental influences lags behind most other autoimmune conditions.

Here we review research to date, from which some evidence has been generated to support a role for breastfeeding, infection and maternal smoking in determining JIA risk.

We also propose further hypotheses worthy of testing, based on knowledge acquired for other autoimmune diseases. These include the role of vitamin D and sun exposure, and the role of early-life infection ('the hygiene hypothesis') in determining risk.

Finally, we discuss future directions including practical study designs to more comprehensively test hypotheses and provide new insight into this important area of research.