Environmental allergen exposure, sensitisation and asthma: from whole populations to individuals at risk

Sensitisation to inhalant allergens remains a major risk factor for asthma,1 but the size of the effect is hotly debated.2,3 Several cross sectional studies have suggested a simple dose-response relationship between dust mite allergen exposure and specific sensitisation, both within communities4–7 and between communities exposed to differing levels of mite allergens.8 The threshold concentration of 2 μg Group 1 mite allergen per gram of dust for developing mite sensitisation in children at high risk has been suggested, but a much higher cut off level of 80 μg/g appeared significant in low risk children.4 For other allergens the relationship between exposure and sensitisation is less well defined. Several studies in the US inner city areas reported that children are more likely to become sensitised to cockroach with increasing cockroach allergen exposure,9 and that high exposure to mouse allergen appears to be associated with an increased prevalence of sensitisation to mouse.10 Some studies in older children and adults reported a close relationship between specific allergen sensitisation and current domestic exposure for mite and cockroach, but not cat allergen.5,11 This, together with studies reporting a protective effect of high cat allergen exposure on sensitisation,12,13 raises the question of whether the dose-response relationship between exposure and sensitisation may be different for different allergens. However, there are remarkably few published data on the longitudinal relationship between allergen exposure and the development of specific sensitisation.

EVIDENCE FROM LONGITUDINAL STUDIES

Several observational birth cohort studies investigating risk factors for the development of allergen sensitisation and asthma have measured allergen levels in dust samples collected in early life to examine the association between allergen exposure and the …