Sept. 30, 2010 -- Your choice of family pet may help determine whether your child develops eczema if he or she is at high risk.
The simple take-home message is that dogs just might make better pets than cats if the goal is to lower an at-risk child’s chances of developing eczema, says lead researcher and University of Cincinnati assistant professor of medicine Tolly Epstein, MD.
Dogs, Cats, and Eczema
Between 10% and 20% of infants and young children develop eczema, a skin condition characterized by inflamed, itchy patches of skin. Like asthma and allergies, eczema is an atopic condition, meaning that it is closely linked to allergen hypersensitivity.
Family allergy history is a strong predictor of whether a young child will develop eczema. About one in four children whose mothers have allergies develop eczema, according to the Asthma and Allergy Foundation of America.
Allergic reactions to certain foods, especially eggs, are strong predictors of whether a child will develop eczema, but the impact of non-food allergens like pet hair is not well understood.
In the newly reported study, Epstein, co-author Grace K. LeMasters, PhD, and colleagues followed 636 children at high risk for developing asthma, allergies, or eczema from birth until after their fourth birthdays.
The children were enrolled in a larger, ongoing study examining the impact of air pollution on childhood allergies.
The children were tested for 17 different allergies annually from age 1 through age 4, and their parents completed yearly surveys.
When the researchers examined which children had developed eczema by age 4, they found that children who were allergic to dogs were less likely to develop the skin condition if they had a dog in the home during their first year of life.
Children with dog allergies who did not own dogs were four times more likely to develop eczema, compared to allergic children without dogs.
Compared to children living with dogs, children who tested positive for cat allergies after age 1 were 13 times more likely to develop eczema by age 4 if they lived with a cat in their first year of life.
Living with a dog was slightly protective for children who were not allergic to them, although the impact was not statistically significant.
Not Clear Why Dogs Are Protective
It is not clear why having a dog in the home may protect at-risk children from developing eczema.
Earlier findings from the same study showed dog ownership to be associated with less wheezing during infancy.
The thinking then was that the outcome supported the so-called "hygiene hypothesis," which holds that exposure to germs early in life protects against allergic disease later on.
But Epstein says the latest analysis suggests something more may be going on.
The researchers measured levels of the allergy-inducing components of dust, known as endotoxins, in the children’s homes and found the protective effect of dog ownership to be independent of these levels.
Pediatric allergy specialist and researcher Dale Umetsu, MD, PhD, calls the study ‘intriguing,’ but he says more study is needed to confirm the findings.
Umetsu is a professor of medicine at Harvard Medical School and a physician at Children’s Hospital Boston.
“Having dogs in the home very early in life may have some benefits for at-risk children, but I would not say this study alone proves this,” he says.
He points out the study and others examining the effect of pet ownership on allergic disease have focused on exposure in the first year of life.
“In our clinic, we see older children who already have asthma or eczema,” he says. “At this point, if there is a pet in the home and the child is allergic that tends to cause more problems.”