(RxWiki News) Parents of newborns usually don’t want their children around cockroaches, rodents or cats. New research suggests that exposure to those creatures may not be as harmful as once thought — it may even be beneficial.
A recent study found that exposure to these creatures and other allergens (substances that trigger allergies) before the age of 1 year may offer some protection against allergies and asthma later in life.
"See a pediatrician if your child starts to wheeze."
This research was led by Susan V. Lynch, PhD, of the University of California, San Francisco.
The researchers were not sure what they would find, but they wanted to investigate how many allergies and wheezing-related problems would be associated with raising children in housing where they were exposed to a variety of things that may cause allergies.
Wheezing is a high-pitched whistling sound produced in the airways that indicates breathing problems.
The researchers thought indoor pollutants could be a source of breathing problems for infants exposed at a young age. On the other hand, previous research has suggested that children raised on farms might be protected against allergies and breathing issues as they grow.
Dr. Lynch and colleagues enrolled 478 children who participated in the study from before birth until at least 3 years of age. The children were from Baltimore, Boston, New York and St. Louis. To be included, the children had to be raised in an area where more than 20 percent of the population lived below the poverty level. They also had to be born at 34 weeks gestation or later, and their mother or father had to have an allergic condition, as allergies are often passed down through families.
The mothers answered a questionnaire before giving birth and every three months afterwards. These mothers and their children also visited the clinic when the child was 12, 24, 33 and 36 months of age.
In a separate look at bacteria found in dust in the home, a researcher visited the home of 104 of the children to do an environmental survey and collect dust when the child was 3 months old and then annually.
All of the children's blood levels were checked each year for antibodies that signaled allergic reaction. At 33 months of age, the children were skin prick tested for 14 common allergens. Skin prick testing is when a tiny amount of a common allergen, such as egg or cat dander, is inserted in the skin. If the skin reacts (redness, swelling, or a rash) to the test, it suggests an allergy.
Cumulative allergen exposure over the first three years of life was associated with sensitization to that allergen (when a child came into contact, he or she developed allergic symptoms), and these children were prone to developing recurrent wheeze.
Children exposed to a wide variety of bacteria found in the house dust were less likely to develop allergies or asthma than children raised in homes with less bacteria, the researchers found.
At the end of three years, 44 percent of the children were sensitized (reacted) to at least one allergen, 36 percent of the children had recurrent wheeze, and 9 percent had eczema (a skin reaction to an allergen in which the skin develops redness or a rash or becomes itchy).
A total of 12 percent of the children met criteria that indicated they would likely develop asthma as they grew.
However, the major finding from this study was that high levels of cockroach, mouse, and to a lesser extent, cat allergen in the first year of life was associated with lower odds of recurrent wheeze at age 3 years. So, exposure before the age of 1 offered protection from the development of allergies in these children, the authors noted.
Being exposed to more than one possible allergen — for example, exposure rodents and cats rather than just cats — offered even more protection for the child.
Wheezing was found to be three times more common among children who grew up without exposure to such allergens than among children who were exposed to all three allergens (roaches, rodents and cats).
The researchers did not find a protective effect from being exposed to either house dust mites or dogs.
Furthermore, children who were exposed to the allergens after age 1 were not protected from developing allergic or asthmatic problems as they grew. This finding was only related to children exposed before they were 1 year of age.
The finding that exposure to rodents, roaches and cats was protective against wheezing and allergic diseases “supports a mounting body of evidence that exposures in the first few months of life are important in shaping allergic and respiratory outcomes,” the authors wrote.
In a press statement, Robert Wood, MD, one of the study's authors, said, "Our study shows that the timing of initial exposure may be critical. What this tells us is that not only are many of our immune responses shaped in the first year of life, but also that certain bacteria and allergens play an important role in stimulating and training the immune system to behave a certain way."
The investigators concluded that their findings may help researchers develop tools to prevent allergies and wheezing in children in the future.
This study was published June 6 in the Journal of Allergy and Clinical Immunology.
The authors disclosed a number of potential conflicts, including that several of the study authors have received funding for consultations given to a variety of different pharmaceutical companies.
The National Institutes of Health funded this study.