A number of studies in the past decade found that exposure to furry pets (e.g., cats, dogs) in the first year of a child's life is important for preventing later allergies (animal, food, pollen). A recent large study from Japan found that exposure to pet cats and dogs during pregnancy (developing fetus) and the first year of life confirms that furry pet exposure is important in reducing the risk of food allergies until at least 3 years of age.
While pet dogs kept inside had a protective effect, pet dogs kept outside did not. Also, the type of pet was important. Indoor pet dog exposure reduced the number of children with egg, milk, and nut allergies, while cat exposure was associated with fewer egg, wheat, and soybean allergies. However, these beneficial results did not apply to pet hamsters, birds, and turtles.
Why is this happening? It's thought that early in life exposure to furry pets (dander, microbes) helps train the developing immune system. Their gut microbes also have differences. By the way, other studies found that exposing a child in the first year of life to potential problem foods (e.g., peanut butter, eggs) reduces the incidence of that specific food allergy.
From Science Daily: Living with pet cats or dogs is associated with fewer food allergies in young children, study finds
In an analysis of over 65,000 infants from Japan, children exposed to pet cats or indoor dogs during fetal development or early infancy tended to have fewer food allergies compared to other children, according to a study published March 29, 2023 in the open-access journal PLOS ONE by Hisao Okabe from the Fukushima Regional Center for the Japan Environment and Children's Study, Japan, and colleagues.
Across some high-income countries, more than one in ten children are diagnosed with food allergies, and the incidence of food allergies in children continues to rise. Previous research has suggested a potential link between dog or farm animal exposure in pregnancy and early childhood and the reduction of food allergies.
In this study, Okabe and colleagues used data from the Japan Environment and Children's Study (a nationwide, prospective birth cohort study) to study 66,215 children for whom data on exposure to various pets and food allergies were available. About 22 percent were exposed to pets during the fetal period (most commonly indoor dogs and cats). Among children exposed to indoor dogs and cats, there was a significantly reduced incidence of food allergies, though there was no significant difference for children in households with outdoor dogs.
Children exposed to indoor dogs were significantly less likely to experience egg, milk, and nut allergies specifically; children exposed to cats were significantly less likely to have egg, wheat, and soybean allergies. Perhaps surprisingly, children exposed to hamsters (0.9 percent of the total group studied) had significantly greater incidence of nut allergies.