The Allergy Epidemic - Where is it coming from?
Author: Thomas C. Beller, M.D.
It seems that everywhere you look today, the prevalence of allergies is increasing. People are suffering more and more from the effects of pollen and other environmental allergies. The sense of happiness that spring flowers used to bring has been replaced by a sense of dread for many as the expectations of sneezing, nasal congestion, itchy eyes and sinus infections takes precedent.
Gone also are the days when food allergies were rare, and here are the days when virtually every school in the country has a policy on how to deal with these dangerous allergies. Peanut allergies have become so commonplace that many schools have separate lunch tables for peanut allergic children and many principals’ offices have a supply of EpiPens®, the device used to reverse severe allergic reactions.
If you haven’t noticed this dramatic increase in allergies, look at some of these U.S. statistics:
Peanut allergy increased by 350% from 1997 to 2008
The cost of allergic rhinitis increased from $2.7 billion in 1995 to $7.3 billion in 2002
10,000 students miss school every day due to allergic rhinitis
3.4% of children had asthma in 1982 while an estimated 15% have it today.
The prevalence of atopic dermatitis (eczema) tripled from 1960 to 1990.
It is hard to deny that we are in the midst of an allergy epidemic. Why is this happening? The leading theory is something called the hygiene hypothesis. If you look at the areas of the world where allergies are common, it becomes clear that developed areas have a much higher prevalence of allergies than underdeveloped areas. English speaking societies are plagued the most. Many signs point to excessive hygiene as the reason. The status of the drinking water supply appears to be a particularly big factor. The cleaner the water supply, the more likely there are to be allergy sufferers. It seems that the more we escape a particular variety of infections, specifically worms and parasites, the more likely we are to develop allergies.
Understanding why this happens becomes somewhat simpler if you examine the problem closely. First, we have to remember that our bodies were designed to identify and attack a large variety of infectious organisms. When our natural defense system has been trained to fight a specific group of organisms that have been present since the dawn of time, it’s not hard to imagine that it might become confused when that group of organisms is suddenly taken away. In this confused state, our immune system goes into search mode and amplifies the searching process, seeking out the worms and parasites it expects to find. When this happens, it is prone to making mistakes, and this mistake is what leads to allergy.
When our immune system has identified a benign substance that it thinks is a parasite, we have developed an allergy. In this setting, further exposure to this benign substance leads to a variety of inflammatory conditions, such as allergic rhino conjunctivitis, asthma, food allergy, and allergic eczema.
The evidence for mistaken identity as the mechanism of allergy is strong. To see this, you have to understand the way our immune system deals with the invasion of worms and parasites. Once you understand this, you will see the similarities between the anti-parasitic response and allergy.
The mechanism our immune system uses to attack worms and parasites is very different from the way it attacks other infections, such as viruses and bacteria. It uses a unique antibody called Immunoglobulin E (IgE) and a unique cell called a mast cell. When a worm or parasite invades the body, IgE recognizes certain proteins on the parasite and triggers the mast cell to release histamine. Histamine has specific functions that are helpful at blocking parasitic invasion and multiplication. First it is designed to release fluid from blood vessels in order to create a rapid swelling type of response. This swelling allows the immune system to surround the parasite for further attack. Parasites and worms are considerably large infections for the immune system to handle, and this surrounding mechanism is a critical part of containing them. It also causes itching, the purpose of which is not perfectly understood, but perhaps functions to alert the infected host of its presence. Next, it has effects that limit access of common pathways parasites use to invade the body, specifically through the respiratory and gastrointestinal (GI) tracts. In the GI tract, it increases acid production in the stomach to kill parasites and activates various gastrointestinal processes to cause diarrhea and vomiting, thus expelling the parasites. In the lungs it causes significant mucous production to create a protective barrier from invasion. It also causes muscular contraction of the bronchioles and swelling of the larynx to reduce air intake temporarily, thus limiting access through the respiratory route.
The allergic response mimics this anti-parasitic response. IgE antibodies, mast cells and histamine are also exactly the same weapons used to attack allergens. When we evaluate the symptoms of a patient to determine if they are allergic in nature we look for these effects of histamine. This is especially true with the most severe type of allergic reaction called anaphylaxis. When a patient experiences anaphylaxis, he or she has diffuse dilation of blood vessels causing diffuse swelling. Itching and hives are often present in the skin (a hive represents this swelling response occurring superficially in the skin). Because the dilation of blood vessels is diffuse, blood pressure can drop significantly causing diminished blood flow to the brain. When the drop in blood flow is severe, we call this anaphylactic “shock.” Severe anaphylaxis also causes nausea, vomiting, diarrhea, bronchospasm and swelling in the throat. All of these effects are related to the release of histamine and other similar weapons that have been historically used to fight parasites.
Even allergic rhinitis shows remnants of the anti-parasitic response. Nasal congestion, runny nose and sneezing are all mechanisms our body would use to dispel parasites trying to invade through the nose.
Because hygiene is becoming an increasing part of our society and is increasing worldwide, we can expect allergic diseases to increase, at least in the short term. However, as our understanding of the problem increases, so is the likelihood that we can solve the problem and devise a way to reverse this troublesome epidemic.
Thomas C. Beller, M.D. specializes in allergy/immunology, internal medicine and clinical and laboratory immunology. For more information, call (843) 689-6442 or visit hiltonheadallergy.com.