What Allergy Is (and Isn’t)
Before I began researching this book, I had no idea just how massive the problem of allergy truly is. Approximately 40 percent of the entire human population already has some form of allergic condition. And by 2030, experts estimate that statistic will increase to 50 percent. But before we can dive more deeply into what these numbers might mean, and why allergies are projected to rise over the next few decades, we need to answer a more basic and fundamental question: What exactly is an allergy?
When I first started talking with scientists and allergists, I assumed I knew what an allergy was. If someone had quizzed me, I would have said, confidently, that an allergy was a negative bodily response to something a person had eaten, touched, or inhaled. If pressed for more details, I probably would have trotted out what I had learned long ago from an introductory biology course—that the human immune system is similar to a defense system. It reacts to foreign substances, such as viruses, bacteria, and parasites, and helps to protect us against infection. But in people with allergies, that same immune system is triggered by something in the environment—like pollen or milk or nickel in metal jewelry—that is harmless to nonallergic people. I would have listed sneezing, runny or stuffy nose, coughing, rashes, redness, hives, swelling, and difficulty breathing as possible symptoms.
Whenever I ask normal people (i.e., not scientists or biomedical experts) to explain what an allergy is, I usually hear something similar to my own initial definition. People of all ages and backgrounds tend to think of allergy and allergens as, as one young nonallergic man described them to me: “Some sort of imbalance with whatever is entering your system. It just doesn’t mesh well with whatever is in your body and it causes your body to try to get rid of it.” Another man described allergy as the body being “self-destructive” when it doesn’t know how to handle something like pollen or a particular food. In one memorable interview, a man with several allergies who had grown up in Chihuahua, Mexico, near the Texas border, suggested that his body is in a constant defense mode—but sees this as primarily positive. He thinks of himself as well defended and described his body as more “careful” and alert than the bodies of nonallergic people. These are all more or less accurate depictions of allergic-type immune responses and they work well enough . . . until they don’t.
Even people who have allergies don’t always understand what, in exact terms, they are or how to distinguish them from nonallergic conditions with similar symptoms.
Take “Chrissie,” for example, one of the first allergy patients interviewed for this book. By the time we spoke, Chrissie had been coping with respiratory allergy symptoms, hives, sporadic swelling of her eyes, and frequent stomach issues for years. She had been diagnosed with hay fever, or seasonal allergic rhinoconjunctivitis, and occasionally visited an ear, nose, and throat specialist (ENT) for treatment when her symptoms changed or worsened. She also experienced gastrointestinal symptoms and skin rashes if she accidentally consumed milk or gluten. Years ago, Chrissie went to see an allergist and was tested for reactions to the most common allergens. Her skin was completely nonreactive to all food allergens, and the allergist told her that it was extremely unlikely that the symptoms she experienced were due to a food allergy. Chrissie’s ENT has repeatedly encouraged her to get retested, but she hasn’t; instead, she goes online to research her symptoms and crowdsource possible remedies.
When asked to define what an allergy is, Chrissie said that it is what happens when the body can’t handle something, especially if the body has come into contact with something too often or in too great of a quantity. Over time and with repeated exposure, she explained, the body ceases to be able to process those things, giving rise to symptoms like her own. She doesn’t believe the results of her skin tests for food allergens and insists that she has a food allergy; since wheat and milk are ingredients in most foods, she posits that her body has learned to reject them over decades of consuming them.
I am beginning this chapter with Chrissie’s story—her misconception of what an allergy is and isn’t, and her palpable confusion and frustration—to illustrate what we typically get right about allergy as well as what we typically get wrong. When it comes to her respiratory allergies, Chrissie is correct in thinking that her body is responding to something that it has had repeated exposure to, but she is wrong about her body being unable to process pollen. (As we’ll soon see, it’s more that her body isn’t able to tolerate it or ignore it.) Chrissie likely doesn’t have a true food allergy, despite having very real symptoms, because she doesn’t show any sensitization to milk or gluten (as evidenced by the results of her skin-prick test). In other words, her immune system is likely not reacting to the foods she’s ingesting. Her immune system is reacting to pollen, however, which causes her hay fever. What Chrissie is really confused about, then, is the difference between an intolerance (in this case, to certain foods, possibly caused by another condition like irritable bowel syndrome or a lack of the enzyme lactase that aids in breaking down the lactose in milk products) and an allergic response (to airborne allergens). And who could blame her? Even as a medical anthropologist with a decent understanding of immunology, I had to discover some of these distinctions the hard way.
The deeper I waded into the scientific literature on allergy and the more conversations I had with allergists and immunologists, the murkier the definitional waters got. To my initial surprise and frustration, the more I learned about how the intricacies of our immune system function, the harder, and not easier, it was to understand allergy. It turns out that what we commonly refer to as “allergy” is actually a grab bag of various conditions. The one thing they all have in common is this: They all involve a hypersensitive immune system reaction to an otherwise innocuous substance—an allergen—that doesn’t typically produce any immune response in nonallergic people. The symptoms of an allergy vary depending on how the allergen enters the body (via the skin, airway, or intestinal tract), the individual genetics of the person, and the many different “allergic pathways” the allergen can trigger.
So, then, what is an allergy? It’s a harmful immune-mediated hypersensitivity reaction to a harmless antigen, which is defined as any toxin or foreign substance that activates an immune response. That’s the technical scientific definition, but it likely doesn’t mean much to you—yet. To fully comprehend what an allergy is, we have to understand how the definition of the term itself shifted and changed over the past century. The concept of allergy is just over a century old, born out of early studies of the function of the mammalian immune system.
In the end, and as you’ll soon see, I learned that an allergy is perhaps best defined by what biological processes it sets in motion.