Ah, spring – the season of grass growing, flowers blooming, and trees sprouting new leaves. But for those with allergies, this explosion of new life probably inspires more dread than joy. Step outside, and within minutes, you’re sneezing, congested, with a runny nose, swollen and watery eyes, and an itchy throat. For you and millions of others, it’s seasonal allergy time. But what’s behind this onslaught of mucus? The answer lies within your immune system.
Seasonal allergies, also known as hay fever or allergic rhinitis, are a hypersensitive immune response to something that’s not actually harmful. Pollen from trees and grass, and mold spores from tiny fungi, find their way into your mucous membranes, and your body attacks these innocuous travelers the same way it would infectious bacteria. Your immune system has a memory. When a foreign substance gets tagged as threatening, white blood cells produce customized antibodies that will recognize the offender the next time around, promptly recruiting the body’s defense team.
However, sometimes the immune system accidentally discriminates against harmless substances like pollen. When it wafts in again, antibodies on the surface of white blood cells recognize it and latch on, triggering the cell to release inflammatory chemicals like histamine. These stimulate nerve cells and cause blood vessels in the mucous membranes to swell and leak fluid, resulting in itchiness, sneezing, congestion, and a runny nose.
Allergies usually, but not always, show up for the first time during childhood. But why do some people get allergies and others don’t? Genetics may be one culprit, as allergies tend to run in families. In fact, errors in a gene that helps regulate the immune system are associated with higher rates of allergies. The environment you grow up in also matters. Being exposed to an allergen as a baby makes you less likely to develop an allergy to it. People who grow up on farms, in big families, and in the developing world tend to have fewer allergies, although there are exceptions due to genetics.
One theory, called the hygiene hypothesis, suggests that when the immune system isn’t exposed to the familiar cast of microbes, it’ll keep itself busy mounting defenses against harmless substances like pollen. Another theory proposes that an immune system toughened up by a barrage of pathogens is less likely to overreact to allergens.
Pollen is a common offender because we encounter so much of it, but there’s a long list of substances – dust, animal dander, insect venom, medications, certain foods – that can send your immune system into overdrive. Some of these reactions can be scary, developing into full-blown anaphylaxis, which typically brings on severe swelling, shortness of breath, and very low blood pressure, potentially being deadly. The body can even have an allergic reaction to itself, causing autoimmune disorders like multiple sclerosis, lupus, and type 1 diabetes.
Even non-life-threatening allergy symptoms can make you miserable, so what can you do about it? Medications can help reduce the symptoms. The most common ones, antihistamines, keep histamines from binding to your cells, stopping the inflammation response. Steroids can help dial down the immune system. Another more permanent option is immunotherapy, where deliberate, controlled exposure to gradually increasing amounts of an allergen can teach the immune system that it isn’t dangerous after all.
And if you’re really adventurous, there’s a less traditional option: intestinal parasites. When hookworms sink their teeth into the intestinal wall, they secrete chemicals that blunt the immune system. Some studies suggest that hookworms can treat allergies, which may be another reason allergies are more common in industrialized countries where hookworms are few and far between.
Of course, you can always just wait your seasonal allergies out. The spring pollen onslaught dwindles by mid-summer, just in time for ragweed season.