FRIDAY, June 6, 2014 (HealthDay News) -- Cleanliness may be next
to godliness, but a home that's too clean can leave a newborn child
vulnerable to allergies and asthma later in life, a new study
Infants are much less likely to suffer from allergies or
wheezing if they are exposed to household bacteria and allergens
from rodents, roaches and cats during their first year of life, the
The results stunned researchers, who had been following up on
earlier studies that found an increased risk of asthma among
inner-city dwellers exposed to high levels of roach, mouse and pet
droppings and allergens.
"What we found was somewhat surprising and somewhat contradictory to our original predictions," said study co-author Dr. Robert Wood, chief of the Division of Allergy and Immunology at the Johns Hopkins Children's Center in Baltimore. "It turned out to be completely opposite -- the more of those three allergens you were exposed to, the less likely you were to go on to have wheezing or allergy."
About 41 percent of allergy-free and wheeze-free children in the
study grew up in homes that were rich with allergens and bacteria.
By contrast, only 8 percent of children who suffered from both
allergy and wheezing had been exposed to these substances in their
first year of life.
The study was published June 6 in the
Journal of Allergy and Clinical Immunology.
The findings support the "hygiene hypothesis," which holds that
children in overly clean houses are more apt to suffer allergies
because their bodies don't have the opportunity to develop
appropriate responses to allergens, said Dr. Todd Mahr, an
allergist-immunologist in La Crosse, Wis., and chair of the
American Academy of Pediatrics' Section on Allergy &
Prior research has shown that children who grow up on farms have
lower allergy and asthma rates, possibly due to their regular
exposure to bacteria and microbes, the researchers noted in
"The environment appears to play a role, and if you have too clean of an environment the child's immune system is not going to be stimulated," Mahr explained.
As many as half of all 3-year-olds in the United States suffer
from wheezing illnesses, and recurrent wheezing and allergies are
considered a risk factor for asthma in later life, researchers
said. According to the American Lung Association, asthma remains
one of the most common pediatric illnesses, affecting about 7
million American children.
The new study involved 467 inner-city newborns from Baltimore,
Boston, New York City and St. Louis. Doctors enrolled the babies in
the study while they were still in the womb, and have been tracking
their health since birth, Wood said.
Investigators visited the infants' homes to measure the levels
and types of allergens. They also collected dust in about a quarter
of the homes and analyzed its bacterial content.
They found that infants who grew up in homes with mouse and cat
dander and cockroach droppings in the first year of life had lower
rates of wheezing at age 3, compared with children not exposed to
Wheezing was three times as common among children who grew up
without exposure to such allergens, affecting 51 percent of
children in "clean" homes compared with 17 percent of children who
spent their first year of life in houses where all three allergens
Household bacteria also played a role, and infants in homes with
a greater variety of bacteria were less likely to develop allergies
and wheezing by age 3.
Children free of wheezing and allergies at age 3 had grown up
with the highest levels of household allergens and were the most
likely to live in houses with the richest array of bacterial
species, researchers found.
"The combination of both -- having the allergen exposure and the bacterial exposure -- appeared to be the most protective," Wood said.
Both Wood and Mahr cautioned that these findings need to be
verified, and that parents shouldn't make any household decisions
based on them.
For example, parents shouldn't adopt a dog or cat assuming that
its presence will help immunize their kids against allergies and
asthma, Wood said. At the same time, they shouldn't ditch their
family pet, either.
"We would not take any of this as information we could use to give advice," Wood said. "Please don't get an intentional cockroach infestation in your house. There's no reason to think that would help."
There are a number of other factors that could influence the
likelihood that an inner-city kid will develop asthma, including
tobacco smoke, high levels of household stress, or even exposure to
the same sort of potentially beneficial allergens too late in life,
past their first birthday, Wood said.
"This is by no means a simple story," he said. "There could be a lot of factors going on."
Mahr said the findings could someday lead to treatments that
would help infants build up resistance to allergies. "I can see
someone coming up with a spray. You'd spray the crib that the kid
sleeps in every so often, and let the kid crawl around in it," he
Find out more about indoor allergens at the
American Academy of Allergy, Asthma &
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