Studies have found that dogs raise levels of 56 different bacterial species that can be found indoors, making the population of indoor microbes more diverse, NYTimes.com reported. While the prospect sounds horrifying for germophobes, being exposed to bacteria from dogs can actually be beneficial for humans.
For one, exposure to animal bacteria may have a positive effect on human moods. "Exposure to animal bacteria may trigger bacteria in our gut to change how they metabolize the neurotransmitters that have an impact on mood and other mental functions," Jack Gilbert, University of Chicago Microbiome Center Director, was quoted as saying in the report.
This could account for the anti-depressant effect that pet companionship has on humans, which was previously just attributed to the release of oxytocins.
Exposure to the bacteria brought in by dogs is also good for the immune system, particularly among kids. The report said that children who grew up exposed to dogs are less likely to come down with autoimmune diseases such as asthma and allergies because their immune systems have been exposed to more bacteria, making them stronger. Yale environmental engineering professor Jordan Peccia said that allergies are a sign of a poorly-calibrated, overly-sensitive immune system, one that attacks contaminants that it shouldn't attack. According to him, being exposed to animal micro-organisms early in life -- particularly during the first three months -- stimulates the immune system early on, allowing it to better distinguish between bad and good bacteria.
Such findings align with the hygiene hypothesis, which suggests that not being exposed to enough bacteria in childhood actually weakens the body's immune system. The hypothesis, which was introduced in the late '80s by immunologist David P. Strachan, was explained through a bodybuilding analogy in an article on LiveScience.com. The article likened the immune system to bodybuilders, who build their strength by lifting increasingly heavy weights. In the same way, the immune system has to "train" by being exposed to contaminants that they must fight off.
Many other studies support the hygiene hypothesis. Among these is a late '90s study by Erika von Mutius, a health researcher who, in comparing allergy and asthma rates in East and West Germany, found that children from dirtier, more polluted East Germany had less allergic reactions and asthma cases compared to those in West Germany.
Another study, published in the New England Journal of Medicine, found that rates of asthma were lower in Amish children than in Hutterite children. While both groups have similar genetic material and lifestyles, the Amish follow only traditional farming techniques and therefore have more contact with farm animals compared to Hutterites, who make use of modern farming methods.
Striking a healthy balance between hygiene and contaminant exposure may be tricky for parents, but it can be done. While regular cleaning and disinfecting is recommended by the Centers for Disease Control and Prevention (CDC), encouraging children to play outdoors, get dirty, and interact with pets may help in strengthening their immune system.
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