Allergies and the Immune System
When we think of allergies, the first thing that might come to mind are the warning labels on the back of prepackaged snacks: produced in a facility that processes soy, shellfish, and tree nuts. But just how common are allergies in everyday life, and what makes them warrant such copious food labeling?
Severe allergies affect nearly 3 percent of the adult population. Since sensitization to an allergic trigger occurs during early childhood, approximately 8 percent of children have or will develop an allergy. Fortunately, childhood-acquired allergies tend to go away on their own over time, which explains why the percentage of the adult population with chronic allergies is much lower. Symptoms of an allergic reaction can run the gamut from relatively benign watery eyes, runny nose, and mild rash, to life-threatening respiratory distress, vomiting, extreme swelling, anaphylactic shock, and loss of consciousness. Adults with allergies tend to have a higher proportion of the more worrying respiratory symptoms and often require more intensive emergency care in the instance of allergen exposure.
Because they can present with a variety of symptoms on a spectrum of different intensities, there is no standardized medical definition for allergies. Although it might not completely encapsulate what an allergy is, most physicians will agree with the National Library of Medicine’s working definition of allergies, which states that they are “adverse health effects arising from specific immune responses that occur reproducibly on exposure to a [substance.]”
There are multiple ways a substance can cause ‘adverse health effects’ in the body, so it’s important to spend a moment to differentiate between a true allergy and something like food intolerance.
The traditional allergic response pathway is propagated by an immune system error. Seeing an ingested food as a threat to the body, the immune system trips the wires and sends out a defensive phalanx of white blood cells, which leads to severe inflammation and the narrowing of airways. The severity of an allergy can depend entirely on the amount of irritant a person was exposed to or ingested, whether or not it can permeate epithelial lining, and its stability upon digestion. Some allergic responses can be delayed, with chronic inflammation symptoms only occurring 24-48 hours after contact with the allergen.
Because it doesn’t involve an immune system response, food intolerance is a little different than an allergy. When an untolerated food is consumed, there is an enzymatic response during digestion, which means, in essence, that the body has trouble breaking down the ingested substance. A common example of this type of food intolerance is seen in lactose intolerance, where a person does not have the necessary lactase enzyme to break down dairy products. This can lead to a range of internal discomfort, most often culminating in nausea, vomiting, diarrhea and other adverse gastrointestinal effects, but it is not life-threatening in the way that true allergies can be.
As dwellings worldwide become increasingly sterilized, allergies of all kinds are becoming increasingly more prevalent, especially in developed, urban environments. According to the hygiene hypothesis, first proposed in an article in the British Medical Journal in 1989, decreases in family size and widespread improvements in personal hygiene have led to a hyper-sanitized environment that reduces the immune system’s ability to self-regulate when presented with new allergen-causing microbes, food, and airborne particulates. The hypothesis poses that ultra-sanitized spaces don’t allow a developing immune system enough exposure to potential allergens, thus making it overreact when presented with them for the first time.
What, then, are the most common allergy triggers? In indoor environments, there is a full range of potential food allergies, along with dust mites, cockroaches, mice dander and feces, mammalian pet dander, and mold. Excess dampness and humidity are conducive to mold growth and reduced lung function, and have been shown to significantly contribute to symptoms of nighttime wheezing and shortness of breath. In outdoor environments, there is wood smoke and tobacco combustion, pollens, molds, diesel and industrial exhaust, sulfur dioxide, nitrogen dioxide, and ozone.
If our sterilized indoor spaces are inadvertently causing allergies, what is the best way to protect against them? Scientists are still out on that one, as further research needs to be done. It has been suggested that encouraging exposure to domestic animals and outdoor environments at a young age can help to shape and strengthen a developing immune system.
As far as preventing allergic reactions when an allergy has already been diagnosed, the easiest approach is just to avoid the allergen altogether. Elimination diets, immunotherapy, food substitutions, and medical therapies can all help to reduce the health risk of living with severe allergies as well. Allergen-specific immunotherapy is especially effective for respiratory allergies and utilizes controlled oral administration of an allergen to slowly build up tolerance in a patient over time.
With all of the emerging fields of research dedicated to understand allergy mechanisms, we can be certain that more highly tailored approaches to allergy treatment and management--and possibly even cures--will be available in the future. In the meantime, remember to keep the house clean--but perhaps not too clean.
Food Allergies: The Basics: https://www.sciencedirect.com/science/article/pii/S0016508515001973
International study of asthma and allergies in childhood: https://erj.ersjournals.com/content/erj/8/3/483.full.pdf
Future therapies for food allergies: https://www.jacionline.org/article/S0091-6749(11)00003-0/fulltext
The prevalence of plant food allergies: https://www.jacionline.org/article/S0091-6749(08)00406-5/fulltext
Diagnosing and Managing Common Food Allergies: https://jamanetwork.com/journals/jama/fullarticle/185820
Environmental and occupational food allergies: https://www.jacionline.org/article/S0091-6749(09)01751-5/fulltext