It is often said that one in 3 in developed countries suffer from some of allergy. By the time they are 3 years old half the children in the US suffer from wheezing or asthma. It is often claimed that this is because of the various chemical compounds that modern humans have put into the atmosphere. But I am not so sure that this is the sole cause or even a significant cause. It could be that we are seeing the downside of having an obsession about dirt and being obsessively “antiseptic” with our children.
Our immune systems need to be triggered and challenged if they are to develop. That is well enough known and is the basic fact exploited by the advances in vaccination science. But the corollary is that when we are overprotective with babies – and especially in the first year of life – a lack of exposure to these triggers prevents the immune system from developing some basic resistances and this may lead to the greater incidence of allergies later on.
It could well be that it is the obsessive cleanliness around our infants which is itself the cause of an underdeveloped immune system and the greater prevalence of allergies.
A new paper finds that some exposure to “dirt” early in life is probably a very good thing.
Susan V. Lynch et al, Effects of early-life exposure to allergens and bacteria on recurrent wheeze and atopy in urban children. Journal of Allergy and Clinical Immunology, 2014; DOI:10.1016/j.jaci.2014.04.018
Abstract:
Wheezing illnesses cause major morbidity in infants and are frequent precursors to asthma. We sought to examine environmental factors associated with recurrent wheezing in inner-city environments. ……..
Cumulative allergen exposure over the first 3 years was associated with allergic sensitization, and sensitization at age 3 years was related to recurrent wheeze. In contrast, first-year exposure to cockroach, mouse, and cat allergens was negatively associated with recurrent wheeze (odds ratio, 0.60, 0.65, and 0.75, respectively; P ≤ .01). Differences in house dust bacterial content in the first year, especially reduced exposure to specific Firmicutes and Bacteriodetes, was associated with atopy and atopic wheeze. Exposure to high levels of both allergens and this subset of bacteria in the first year of life was most common among children without atopy or wheeze.
In inner-city environments children with the highest exposure to specific allergens and bacteria during their first year were least likely to have recurrent wheeze and allergic sensitization. These findings suggest that concomitant exposure to high levels of certain allergens and bacteria in early life might be beneficial and suggest new preventive strategies for wheezing and allergic diseases.
From the John Hopkins Press Release :
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 these allergens soon after birth. The protective effect, moreover, was additive, the researchers found, with infants exposed to all three allergens having lower risk than those exposed to one, two or none of the allergens. Specifically, wheezing was three times as common among children who grew up without exposure to such allergens (51 percent), compared with children who spent their first year of life in houses where all three allergens were present (17 percent).
In addition, infants in homes with a greater variety of bacteria were less likely to develop environmental allergies and wheezing at age 3.
When researchers studied the effects of cumulative exposure to both bacteria and mouse, cockroach and cat allergens, they noticed another striking difference. 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. Some 41 percent of allergy-free and wheeze-free children had grown up in such allergen and bacteria-rich homes. 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.
Not all dirt is bad.
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