The ‘hygiene hypothesis‘ and the Development of Multiple Sclerosis

SUMMARY We review evidence linking inadequate microbial exposure in early life to the development of multiple sclerosis (MS). There is some supportive, but not conclusive evidence for a role of a hygienic environment in early life and MS. Population-level studies of MS are consistent with the hygiene hypothesis but are limited by methodological issues. Late infection with Epstein–Barr virus (EBV) has been prospectively associated with MS and must be incorporated into any model where the hygiene hypothesis is implicated in the development of MS. One possibility is that inadequate microbial exposure in early life contributes to a dysregulated host immune response to EBV. Two areas of particular interest include the potential role for helminthic infection in biasing the human immune response away from the immune profile associated with MS and also the role of microbial exposure in training the development of the EBV-specific immune response.