Improved hygiene and reduced exposure to microbes have both been suggested as possible causes of the rapid rise of atopy in Western societies. But previous studies have presented results that argue both for, and against, such a hypothesis. In 7 April The Lancet Marko Kalliomäki and colleagues from Turku University Hospital in Finland suggest that specific microbes in the commensal gut microflora can prevent atopic disease.

In a double-blind randomised placebo-controlled trial, Kalliomäki et al gave daily doses of 10¹⁰ colony forming units of Lactobacillus GG prenatally to mothers with a family history of atopy and postnatally, for 6 months, to their infants. The frequency of atopic eczema in the Lactobacillus GG group was half that of the placebo group (15/64 [23%] vs 31/68 [46%] (Lancet 2001, 357:1076-1079).

In atopic individuals the characteristic T-helper-2-dominant immunity present from birth is intensified, leading to the subsequent development of atopic...