As our hygiene and cleanliness improves it seems we become more susceptible to allergies. It's as if our immune system is yearning for action, but having no enemies in the form of infectious agents or parasites to battle, it targets harmless substances present in the environment. This constitutes an allergic reaction. Central to this reaction are specialized proteins known as antibodies. Specifically, IgE (immunoglobulin E) antibodies are implicated. They are made when a foreign substance enters the body and then attach themselves to immune cells called mast cells where they lie in wait, ready for action should the intruder appear again. When the allergen does appear, the antibodies recognize it and bind to it. This disturbs the structure of the mast cell, causing it to "wake up" and release various disease-fighting molecules. The prime one is histamine. This molecule, when released, makes local blood vessels more permeable and unleashes the symptoms of an allergy. There's sneezing, sniffling, watery eyes and all the rest as the body tries to rid itself of the troublesome allergen.
Today our hygiene-obsessed society is focussed on the use of antibacterial soaps, sponges, pillows and even toys. Some people carry around a special germ-killing lotion and slather it on at the first sign of 'contamination'. Sounds like something out of a sci-fi movie. You greet someone, shake hands and then immediately proceed to cleanse yourself of them with some goo. But this could end up causing more harm than good. Not only does this over-use of antibacterial products breed drug-resistant forms of microorganisms, it may also be contributing to the rising incidence of allergies in our society.
When we're born, our immune system is considered 'naive.' White blood cells, such as the helper T cells, haven't yet fully developed. There are actually two types of these T cells. Th1 cells fight mostly small invaders like bacteria and viruses which directly attack our cells while Th2 cells are designed to fight the bigger enemies, such as parasites and worms which may lurk in-between cells. It turns out that these Th2 cells are also the cells that initiate IgE production. Therefore it is not surprising that allergy-prone people tend to have more Th2 cells while those without allergies have more Th1 cells. This may be because of the lack or the presence of microorganisms in the environment of a growing child. Here's the theory then: if there aren't many 'bugs' around, a child doesn't make as many Th1 cells and so ends up making an excess of Th2 cells which tend to overreact to normally harmless substances such as pollen, dust or certain foods by stimulating IgE production. At birth the Th2 cells are the most likely to be triggered into activity. And if the Th1 cells aren't sufficiently stimulated, by microorganisms as found in dirt, for example, allergies can result. Th1 cells produce signals that reduce Th2 responses and Th2 cells produce signals that reduce Th1 responses. In other words, there is a delicate balance between these two types of cells.
So we now have a theory of how infections may prevent allergies. We want to get those Th1 cells active so they will curtail the amount of Th2 cells. Rolling in the dirt may do that. But there is another way to prevent Th2 cells from cranking out IgE antibodies. Just don't give them any enemies to fight. As stated before, if there are no parasites to defeat they will jump at other intruders such as food components. Keeping foods such as milk and peanuts away until Th2 activity is naturally reduced by the aging process can therefore reduce the risk of allergies.
Ok, so we want to let kids wallow in dirt and snatch peanut butter sandwiches from their mouth. Will this really work in preventing allergies? In a May 2000 study published in the Lancet, doctors looked at 61 children aged 9-24 months who all had previous asthma-like episodes to see the effects of exposing these kids to house dust. It turns out that those exposed to more dust ended up having higher Th1 cell activity, diverting the immune system from prompting the allergic Th2 reaction. And that means less likelihood of developing asthma. This meshes with 1997 British study published in the journal Science which showed that Japanese schoolchildren who received TB (tuberculosis) vaccines were up to three times less likely to develop allergies. And those who already showed symptoms of allergies showed a decrease in symptoms after being vaccinated. This is probably because the TB vaccine is a weakened version of the Mycobacterium tuberculosis microorganism and when injected, it prompts a strong Th1 immune response from the child, diverting the immune system from allergic Th2 reactions. That's not to say children should run out and try to catch TB, but it wouldn't hurt for them to roll in the dirt a bit so they can come in contact with the harmless forms of mycobacteria.
Clinical experience also tells us that younger siblings are less likely to develop allergies than their older brothers or sisters mostly because the older ones pass on extra germs to the younger ones. And children from bigger families have even less chance of developing allergies likely due to the fact that there are so many different germs floating around. Along the same lines, a German study published in a February 1999 issue of the Lancet found that children who entered daycare facilities at a younger age tended to be less susceptible to later allergies than their older classmates. Another study, this time from Sweden, published in the May 1999 Lancet confirmed that there were fewer cases of allergies in families that avoided antibiotics and vaccinations as much as possible. Both of these studies support the recurring theme of childhood infections reducing rather than prompting allergic reactions.
Dust and dirt may not be the only things you can let sit around your house, pet hair could be good for the kids too. In an ongoing study starting in 1980, Dr. Christine Cole Johnson at the Henry Ford Health System in Detroit found that children who grew up in a house with a pet during their first year of life were significantly less likely to develop allergies to that pet later in life. And it might go even further than that... these same children also showed less likelihood of reacting with ragweed, grass and dust allergens. This is great! Why not just stop cleaning the house altogether and turn it into a zoo?
So let's get this straight, we let the kids roll in the dirt, breathe in the household dust and pet hair, and make sure they are sneezed and coughed on by their older siblings and classmates. Sounds more like we're letting kids be kids. This may be all it takes to keep down the fast increasing numbers of allergic people in the modern world. So next time your child comes home covered in mud or dirt, don't get mad, rejoice in the fact that this dirt may prevent a later onset of hay fever or asthma. Let kids be kids. They were designed to be dirty.
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