By Dr. Becker
Until fairly recently, many people assumed exposing children to dogs and cats is what creates pet allergies.
But according to a number of recent studies, if exposure takes place during the first year or two of life, it can actually protect children against future development of allergic sensitivities.
And what's especially interesting is exposure to pets in infancy can not only reduce the risk for allergies to pet hair and dander, but to certain other environmental allergens as well.
2011 Study: Infants with Cats in the Home Have 50 Percent Fewer Cat Allergies
A study1 published last year in the journal Clinical & Experimental Allergy followed over 550 kids from birth to the age of 18, and regularly gathered data from the children's families about the presence of indoor pets.
At the end of the study, blood samples were taken to test the study participants for allergies to cats and dogs.
The kids who had a cat at home during their first year of life were 50 percent less likely to be jouallergic to cats than the children not exposed from birth to one year.
And a decreased risk of allergy to dogs was revealed in boys who had dogs in the home during their first year.
The same protective effect against dog allergies wasn't as strong in the girls in the study.
Researchers concluded exposure to pets at later ages didn't make much of a difference.
It was exposure during infancy that was important, leading study authors to conclude, "The first year of life is the critical period during childhood when indoor exposure to dogs or cats influences sensitization to these animals."
2009 Study: Kids with Both Cats and Dogs Less Likely to Have Allergies at Age 13
In a 2009 study2, pet ownership between birth and age 9, and between 18 and 32 was investigated. Allergy (skin prick) tests were performed on study participants at 13 and 32 years.
Study results showed children who lived with both a cat and a dog were less likely to have allergies at 13. However, living with just a cat or a dog did not provide the same benefit.
For the kids who were not allergic by age 13, having both a dog and cat in adulthood resulted in lower risk of new allergies by age 32.
2008 Study: Living with a Dog in Early Childhood Protects Against Inhalant Allergies
The objective of a study published in 20083 was to determine if the effects of exposure to pets on immune development and allergies in young children could be explained by changes in exposure to innate immune stimuli in settled dust.
The study authors' conclusion:
Exposure to dogs in infancy, and especially around the time of birth, is associated with changes in immune development and reductions in wheezing and atopy [allergic hypersensitivity]. These findings are not explained by exposure to endotoxin, ergosterol, or muramic acid.
Another 2008 study published in the journal of the European Respiratory Society4 investigated the link between contact with dogs and exposure to endotoxins during infancy, and the development of allergies up to 6 years of age.
Researchers concluded children exposed to a dog in the home during early childhood had a significantly lower rate of mixed pollen and inhalant sensitivity from birth to 6. Interestingly, this study did not find that these children had less sensitivity to dogs despite early exposure.
Kids who had regular contact with dogs, but who did not actually live with one, did not have reduced rates of pollen and inhalant sensitivity similar to the children who lived with dogs in the home.
Study results did not link house dust endotoxin exposure during infancy and development of allergies.
The researchers concluded living with a dog during early childhood protects against inhalant allergies.
2005 Study: Early Cat Ownership Significantly Lowered Cat Allergy and Allergic Rhinitis
A study of children with respiratory symptoms living in Liguria, Italy looked at the link between early cat ownership and development of allergic rhinitis.5
This study, published in 2005, concluded early cat ownership significantly lowered the risk of developing allergies to cats. It was also linked with a significantly lower risk of allergic rhinitis than cat ownership later in life, or no cat ownership.
Study authors' conclusions:
Cat ownership in early childhood can play an important role in preventing sensitization to cat and in lowering the frequency of allergic rhinitis, at least in children with the characteristics of the population studied.
2002 Study: Infants Exposed to 2 or More Dogs or Cats During Their First Year Had Fewer Allergies to Pets, Dust Mites and Ragweed
A study6 published a dozen years ago in the Journal of the American Medical Association evaluated the link between dog and cat exposure in the first year of life and allergic sensitization at the age of 6 to 7.
Researchers concluded children exposed to two or more dogs or cats during their first year were less likely to develop allergies to not only dog and cat hair, but also dust mites and ragweed.
Pet Allergies and the Hygiene Hypothesis
The theory of the hygiene hypothesis, born in the late 1980's, is that the huge increase in allergic disorders in the last century is due in part to our somewhat obsessive cleanliness standards.
Since the advent of anti-bacterial products for every conceivable use, we've become hyper vigilant in trying to avoid every germ in the environment. On the surface this might seem like a sensible approach, but not everyone is convinced.
It is thought that early exposure to bacteria and parasites prepares immature immune systems to fight dangerous infections. Further, this 'priming' of the immune system also helps it learn the difference between serious health hazards like a pneumonia infection, and harmless irritants like pet dander and pollen.
According to the hygiene hypothesis, when the immune system remains naïve from lack of exposure to real pathogens, it is more likely to mount attacks against benign environmental triggers.
It's possible, then, that exposure to pets in the home during the first year of life helps a child's immune system become balanced in terms of recognizing pet hair and dander for what it is -- harmless.
- 1 Clinical & Experimental Allergy, Volume 41, Issue 7, pages 979–986, July 2011
- 2 The Journal of Allergy and Clinical Immunology, Volume 124, Issue 4 , Pages 745-750.e4, October 2009
- 3 Clinical & Experimental Allergy, Volume 38, Issue 10, pages 1635–1643, October 2008
- 4 European Respiratory Journal, May 1, 2008 vol. 31 no. 5 963-973
- 5 Annals of Allergy, Asthma & Immunology, Volume 94, Issue 5 , Pages 561-565, May 2005
- 6 JAMA. 2002 Aug 28;288(8):963-72