Auto-immunity refers to those immune responses that are directed against constituents of the body. Although auto-immune responses are genuinely considered to be adverse processes, they can also develop in a physiological setting.

Collectively, auto-immune diseases are fairly frequent and may affect up to 10% of the human population in industrialized countries. However, individually most auto-immune diseases are rare if not extremely rare. Despite claims that environmental and occupational chemical exposures are likely to be significant causes of auto-immune diseases, convincing laboratory as well as epidemiological evidence is very scarce. In fact, a major hurdle with respect to auto-immunity nowadays is that too little is known of the pathophysiological mechanisms involved to make any definitive conclusion.