Childhood Allergies: Exposure to Animals During Early Childhood Reduces the Risk

It is generally accepted that early exposure to pets helps protect infants against the later development of allergies. Swedish researchers sought to determine whether there is a dose-dependent association between a child’s close contact with cats and dogs during their first year of life and the development of allergies. They found that the prevalence of allergies among children aged 7 to 9 decreases with the number of pets in the household, suggesting a positive protective effect depending on the “dose” of animal exposure.   For the past two decades, it has been widely accepted that allowing very young children to come into direct contact with various allergens (pollen, animals, microbes, etc.) helps strengthen their immune systems, thereby providing them with increased protection throughout their lives. Pets are no longer considered a risk factor for allergies in families with otherwise healthy infants. The existence of a protective effect against allergies has even been clinically demonstrated and corroborated by immunological data. In this new study published in PLOS One, researchers from the University of Gothenburg sought to learn more about the potential benefits of close exposure to pets during the first year of life. The team collected data on the health status of all children aged 7 to 8 in two Swedish cities and on the presence of pets in the household. A total of 1,838 questionnaires on asthma, eczema, and allergic rhinoconjunctivitis were distributed to the families involved, of which 1,029 were returned (a response rate of 56%). In this sample, the researchers found that the incidence of allergies reached 49% among children not exposed to pets. This percentage drops to 43% for children with a single pet at home, to 24% for those living with three pets, and falls to 0% for households with five or more pets. A second data collection effort involved 249 infants from birth, including 28 living on a farm and 37 in rural areas. Parents were interviewed when their children were between 6 and 12 months old, and pediatric allergists conducted clinical tests at 18 months of age and again between 3 and 8–9 years of age. Analysis of these data shows that the allergy rate among children growing up without any pets is 48%, while it is 35% for children with a single pet and drops to 21% for children living with multiple pets. Thus, the Swedish team observed a dose-dependent association between sensitization to animals (as well as to pollen) and an increase in the number of pets in the household: when children aged zero to one year live with multiple pets, they develop fewer allergies and other illnesses later in life. The incidence of allergic diseases decreases as the number of cats and dogs in the home increases, while the protective effect grows. Researchers also suggest that the protective effect provided by pets is not the only way to reduce the risk of allergies. A dog or cat can thus have a protective effect on children who have few other protective factors, provided the child has close, direct contact with the animal during their first year of life. If the child already benefits from several other factors that stimulate the immune system through microbial exposure, a dog or cat may not provide additional protection, unless the child is exposed to multiple animals (the “mini-farm” effect, which is not species-specific).