Infants exposed to two or more cats or dogs during the first year of life appear to be protected against several common allergies later in childhood.
US researchers performed a detailed analysis of the living environment, animal exposure and incidence of allergy in 474 children who were followed from birth until 6-7 years of age.
By age 6-7, the prevalence of any atopic skin reaction to several common allergens, including dustmite, ragweed and bluegrass, was 33.6 per cent in children with no early exposure to pets and 34.3 per cent with exposure to one cat or dog. But the rate dropped dramatically to 15.4 per cent with exposure to two or more cats or dogs early in life.
Blood tests also revealed that children with the highest exposure to animals also had lower levels of IgE (antibody released in allergic reactions).
Scientists theorise that animal allergens present small, manageable challenges to the young immune system, thus 'training' it not to 'overreact' (as with atopy) to allergens later in life (JAMA, 2002; 288: 963-72, 1012-3).