title: Potential role of reduced environmental UV exposure as a driver of the current epidemic of atopic dermatitis.
abstract: The basis for the sudden and dramatic increase in atopic dermatitis (AD) and related atopic diseases in the second half of the 20th century is unclear. The hygiene hypothesis proposes that the transition from rural to urban living leads to reduced childhood exposure to pathogenic microorganisms. Hence instead of having the normal TH1 bias and immune tolerance because of repeated exposure to pathogens, urban dwellers have TH2 cell immune activity and atopic disease in a more sterile environment. Various other environmental exposures have been implicated in the explosion of AD (and atopic disorders in general), including breast-feeding, tobacco smoking, alcohol consumption, and exposure to domesticated furry pets. Notably, the key role of a compromised barrier of neonatal skin as a predisposing factor in the development of childhood AD has recently been demonstrated. In this article we review the salubrious effects of suberythemogenic doses of UVB irradiation for the skin barrier. We then discuss how the lack of sufficient UVB exposure could have contributed to the rapid increase in the incidence of AD in developed countries. This hypothesis offers a separate but not competing partial explanation, which should be viewed as not discounting the role of the etiopathogenic factors that also could influence the prevalence of atopic disorders.
authors: National Allergy Research Centre, Department of Dermato-Allergology, Gentofte University Hospital, University of Copenhagen, Hellerup, Denmark. Electronic address: jacob.p.thyssen@regionh.dk.
authors: Jacob P
authors: JP
authors: Thyssen
authors: Division of Dermatology, Ohio State University, Columbus, Ohio.
authors: Matthew J
authors: MJ
authors: Zirwas
authors: Dermatology Service, Veterans Affairs Medical Center, and the Department of Dermatology, University of California, San Francisco, Calif.
authors: Peter M
authors: PM
authors: Elias
mesh_terms: D000818:Animals; D003876:Dermatitis, Atopic / Q000150:complications / Q000453:epidemiology* / Q000209:etiology; D058872:Epidemics; D000091344:Filaggrin Proteins; D006801:Humans; D061148:Hygiene Hypothesis; D007111:Immunity, Cellular; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D000069079:Radiation Exposure; D018418:Th2 Cells / Q000276:immunology*; D014466:Ultraviolet Rays; D014505:Urban Population
keywords: Atopic dermatitis; UV; filaggrin; irradiation; pathogenesis; phototherapy; skin