A recent report in the journal Nature Reviews Cancer illustrates the dangers of being overcautious about hygiene. This comes as a shock for those parents who don’t allow their kids to have the touch of even a tinge of mud saying it would harm them. The study indicates that children who grow up without exposure to germ cells are more at risk of developing even leukaemia.
The study is not the first of its kind. The Hygiene Hypothesis was proposed more than twenty years ago by Strachan to explain the dramatic increase in the prevalence of allergic diseases and asthma that has occurred over the past two to three decades. What Strachan observed was that the younger children in large families had less asthma and allergy, presumably due to increased exposure to infections that passed around in such large families.
Later, the Hygiene Hypothesis was extended to explain the great increase in the prevalence of inflammatory bowel disease that occurred over the same time period. However, the exact scientific underpinnings for the Hygiene Hypothesis, e.g., the specific infections and the mechanisms by which infections affect the immune system to prevent disease, have remained a puzzle over the years for both scientists and clinicians.
A clear biological explanation for the Hygiene Hypothesis though, may be at hand, as proposed in an article recently published in Science, using mouse models2. Blumberg and his colleagues showed that mice raised under sterile, germ free conditions were more likely to develop experimental colitis, called oxazolone-induced colitis, and more likely to develop an experimental form of allergic asthma.
Importantly, the reestablishment of the intestinal commensal bacteria, collectively known as microbiota, in the germ-free mice with standard mouse colony bacteria prevented their predisposition to severe colitis or asthma. However, the beneficial effects from the microbiota developed only when very young mice were exposed to the bacteria, whereas exposure of adult germ-free mice to the microbiota did not reduce the predisposition to colitis or asthma.
Thus, exposure of pregnant germ-free mice to the microbiota, which then affected the pups when they were born, prevented the later predisposition of the pups as adults to colitis and asthma, consistent with the idea that exposure of young children to germs prevents asthma and allergy.
All these studies indicates only one fact – being overcautious about hygiene would adversely affect health. Let’s let children play with nature. Let them get in touch with even those germs and gain immunity. Nature has its own way of caring children to grow up. The only thing for us to do is to help them grow and protect them until they are fit to face the challenges in the world.