Recent studies do not confirm the 'conventional wisdom' that breastfeeding is protective against allergy and asthma.
Early reduction in childhood wheezing may reflect protection from viral infections.
Breastfeeding and allergies: time for a change in paradigm? Duncan, Joanne M; Sears, Malcolm R. Genetics and epidemiology, Current Opinion in Allergy & Clinical Immunology. 8(5):398-405, October 2008.
Shorter duration and nonexclusivity of breastfeeding are associated with increased risk of asthma symptoms in children. ERJ January 1, 2012 vol. 39 no. 1 81-89.