Figure 7-15 A Swiss cheese model for the causation of autoimmune thyroid disease, showing the effect of cumulative environmental, genetic and existential weaknesses lining up to allow AITD to occur, like the holes in the slices of cheese. In reality each of the slices depicted is composed of many individual components. The Swiss cheese model for accident causation, for instance an airplane crashing, incorporates active failures (e.g. pilot error) and latent failures (e.g. maintenance deficiency). Some factors contributing to the initiation of AITD are latent (e.g. ageing, growing up in a hygienic environment) and others are active (e.g. possession of an HLA allele which permits presentation of a thyroid autoantigen). Reproduced with permission from Weetman AP, Europ Thy J 2013 in press.