Signs are plastered on every other door: “Nut Free Zone!” “No Tree Nuts!” “Pineapple Free Zone!” However colorful they might be, these posters are not for decoration. These are warning signs,  put up to alert whoever enters that what is in their brown-bag lunch could be fatal to another.

“An allergy is your body’s abnormal response to a normal environmental agent,” University of Michigan allergist Marc McMorris explained. “That leads to allergy symptoms and that’s caused by IGE, the allergy antibody. Because, why would you respond to one thing and I wouldn’t? Well, your body’s decided to do that.”

In the past 20 years, the number of people with allergies has nearly doubled. The allergy increase is not just for food allergies either, it’s all across the board: asthma, eczema, allergic rhinitis, hay fever, etc.

Not only are allergies more prevalent, they are staying with children much longer than they used to. The statistics show that 20 percent of peanut allergies will leave, 8 percent of tree nut allergies will go away, and 90-95 percent of milk, egg, wheat, soy will dissipate as children mature.

“The issue is that your generation is delaying that versus the prior generation,” McMorris said. “The milk, egg, wheat and soy used to go away by kindergarten and now it’s late grade school, and I have kids in college who are still anaphylactic to milk. That was unheard of 25 years ago.”

But this increased allergy epidemic is not happening in every part of the world. Parts of the world where there are fairly high rates of illness and infections, such as third world countries, have virtually no allergies.

Dr. McMorris explained that the immune system has basically two fronts. One is to fight illness and germs, bacteria, and viruses, and the other is to look for allergies.

“So, if the immune system doesn’t have to worry about illness as much anymore, it shifts over to the other side,” McMorris said.

In 1989, David P. Strachan, a professor of epidemiology at St. George’s University of London, published a short paper in the British Medical Journal. This paper was about a study he did with British children all born in March 1958. He followed them for 23 years and looked at how many of them developed hay fever. Strachan found that children who had older siblings had fewer allergies, because the younger children are exposed to more illness from their older siblings.

From this study, Strachan speculated a link between early infant illness and the absence ofallergies. This belief has since been dubbed “The Hygiene Hypothesis”, and is one of the theories as to why more people are developing allergies as societies modernize.

The Hygiene Hypothesis argues that as children are immunized and not exposed to illness when they are young, they develop more allergies.

Many studies have been conducted looking at children growing up on farms in relation to how many developed allergies and what kind. Researchers have found that people who grew up on a farm have lower rates of allergies. This is believed to be from the early exposure to lots of bacteria, viruses, and fungi: from the feces of farm animals to the unpasteurized milk that the children drink. The seemingly “dirty” environment that farm kids grow up on actually helps them in the long-run, allergy-wise.

Similar to the farm studies, children growing up with pets, such as dogs and cats, tend to have less allergies.

In the 1990s, in an effort to stop the increase in allergies, allergists recommended waiting for babies to mature more, for a few years or so, before introducing foods with higher allergy risk (eggs, nuts, etc.) However, recent research has shown that introducing high risk foods to babies between five to six months to a year may be better than delaying them.  

“We no longer are advocating delay of exposing babies to high risk foods like we did a year or two ago,” McMorris said.  “And that’s part of a national movement to introduce foods earlier to babies so that they are able to develop tolerance.”

However, the hygiene hypothesis isn’t the only theory that tries to explain the influx of allergy rates.

Vitamin D deficiency could also play a part in the development of allergies. More epipens are prescribed in northern states than in southern states, possibly due to more sun exposure in the South. Some allergists are checking the Vitamin D levels in their patients and have found that patients, who are prescribed Vitamin D supplements, experienced a decrease in their hives, their eczema, etc; but it does not work as well with food allergies.

Additionally, women who are pregnant during winter months have a higher rate of having children who develop allergies than women who are pregnant in summer months because in summer they get Vitamin D, but in winter they get much less.

Ultimately, it also comes down to genetics. If a parent has allergies, there is a 50 percent chance they will pass it on to their child. If both parents have allergies, the risk increases to 70-80 percent. Everybody is programmed in different ways, people with allergies are programmed differently than people without allergies.

“There’s no real good reason why one individual has a peanut allergy vs another individual, or why one person’s allergic to a dog and another person isn’t, it’s just a combination of genetics and environment,” McMorris said.