Early allergen exposure and atopic eczema

Abstract

Background The relationship between exposure to indoor aeroallergens in early life
\nand subsequent eczema is unclear. We have previously failed to show any significant
\nassociations between early life exposure to house dust mite and cat fur
\nallergens and either sensitization to these allergens or wheeze. We have also previously
\nreported a lower prevalence of parent-reported, doctor-diagnosed eczema
\nby age 2 years for children exposed to higher concentrations of house dust mite,
\nbut no other associations with other definitions of eczema or for exposure to cat
\nallergen.
\nObjectives To extend the exposure–response analysis of allergen exposure and
\neczema outcomes measured up to age 8 years, and to investigate the role of
\nother genetic and environmental determinants.
\nMethods A total of 593 children (92Æ4% of those eligible) born to all newly pregnant
\nwomen attending one of three general practitioner surgeries in Ashford,
\nKent, were followed from birth to age 8 years. Concentrations of house dust
\nmite and cat allergen were measured in dust samples collected from the home at
\n8 weeks after birth. The risk of subsequent eczema as defined by the U.K. diagnostic
\ncriteria was determined according to different levels (quintiles) of allergen
\nexposure at birth.
\nResults By age 8 years, 150 (25Æ3%) children had met the diagnostic criteria for
\neczema at least once. Visible flexural dermatitis was recorded at least once for
\n129 (28Æ0%). As in other studies, parental allergic history was positively associated
\nwith most eczema outcomes, as were higher maternal education and less
\ncrowded homes. No clear linear associations between early exposure to house
\ndust mite or cat allergen were found, regardless of the definition of eczema used.
\nThe risk of eczema appeared to increase for the three lowest quintiles of house
\ndust mite allergen exposure (odds ratio, OR 1Æ37 for third quintile compared
\nwith first), and then to fall for the two highest quintiles (OR 0Æ66 and 0Æ71)
\neven after controlling for confounding factors.
\nConclusions The lack of any clear exposure–disease relationship between allergens
\nin early life and subsequent eczema argues against allergen exposure being a
\nmajor factor causing eczema. If the lower levels of eczema at higher levels of
\nhouse dust mite are confirmed, then interventions aimed at reducing house dust
\nmite in early infancy could paradoxically increase the risk of subsequent eczema.