Previous investigations into the effects of early exposure to animals have returned conflicting results. Some retrospective studies reported an increased risk of allergy to dogs and cats following exposure during infancy; others indicated that children raised on farms are less likely than their urban counterparts to be allergic. In the new work, Dennis R. Ownby of the Medical College of Georgia and his colleagues focused on exposure to dogs or cats during the first year of life and subsequent risk of developing sensitivity to common allergens. The team studied 474 healthy infants, following up annually until the children reached six to seven years of age, at which point they were given skin-prick tests and blood tests for allergies to dogs, cats, dust mites, ragweed, bluegrass and a mold known as Alternaria.
The results were striking. After adjusting for confounding factors such as parental smoking and dust-mite allergen levels, the investigators determined that kids who grew up around two or more dogs or cats in the first year of life were 66 to 77 percent less likely to develop allergies than those who were raised in single pet- or no pet-homes. Importantly, early exposure to pets appeared to lower the risk of developing allergies not only to domestic animals but also to other common allergens such as grasses, pollens and molds.
"Other studies have suggested a protective effect of pet exposure on allergy and asthma symptoms, but generally have looked only at whether pet exposure reduced pet allergy," remarks Marshall Plaut of the National Institute of Allergy and Infectious Disease. "This new finding changes the way scientists think about pet exposure; scientists must now figure out how pet exposure causes a general shift of the immune system away from an allergic response." If they can do that, Ownby says, new allergy therapies might not be far off.
