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How seasonal allergies work — and why they make you so miserable

Allan Foster

In recent days, millions of Americans have begun to suffer from runny noses, itchy eyes, and the constant urge to sneeze.

Roughly 25 million Americans suffer from seasonal allergies, and there's one clear culprit for them — plant sperm.

Seasonal allergies are the immune system's response to the millions of pollen grains — plant sperm cells — floating through the air every spring. By incorrectly interpreting pollen as a health threat, your body triggers an inflammatory response, leading to annoying symptoms like itchy eyes or a runny nose. This is known as allergic rhinitis, or "hay fever."

We still don't have a cure for this sort of allergy, although there are medicines you can take to minimize your symptoms. The most effective strategy is simply to limit your exposure to the outdoors on the highest-pollen days.

Here's a complete guide to dealing with your seasonal allergies, along with everything else you could possibly want to know about the weird way our bodies respond when we get in the way of plant sex.

1) Why do I get seasonal allergies?

During the spring and summer, most grasses, trees, and other plants take part in a 240-million-year-old tradition: shooting their sperm cells into the air so that they might get caught by the wind, land on another plant, and fertilize it, eventually producing a seed. Each sperm cell is packaged in a hard protective shell, forming a tiny grain of pollen.

Although these pollen grains are meant to land on other plants, some end up in a different place: inside your nose.

Whoa: pollen grains under a microscope.
Dartmouth Electron Microscope Facility/Wikimedia Commons

For most people, this isn't a big deal. But for about 8 percent of adults, pollen from specific species — including trees like pine and birch, weeds such as ragweed, and various grasses — can trigger a rather unfortunate response from the immune system. Your body mistakenly interprets these pollen grains as foreign intruders and begins a series of steps intended to beat them back:

NIH/Wikimedia Commons

1) White blood cells (called B cells) inside your nasal passages come into contact with pollen grains and mistake them for dangerous interlopers.

2) These white blood cells then produce large numbers of antibodies — small, Y-shaped proteins that are specially designed to lock on to a specific threat (in this case, the pollen grains).

3) The antibodies bind to other kinds of white blood cells (called mast cells and basophils). So the next time grains of pollen enter your nose, the specially designed antibodies recognize and lock on to them, as well, eventually causing the mast cells and basophils to break open.

4) The reason these cells rupture is that they're filled with histamine — a chemical your body uses to battle infections and other health threats through the inflammatory response, in which blood vessels expand and tissues become warm and swollen to speed the healing process. But the large amount of histamine released when the cells rupture in response to a false health threat causes an irritating range of symptoms in your nasal passages and nearby, including itchy, watery eyes, a runny nose, and frequent sneezing.

2) Why do some people suffer from these allergies while others don't?

The short answer: we really don't know.

Genetics are at least part of the reason — having a parent with a pollen allergy makes it more likely you'll have one as well. And scientists have begun identifying some genes that seem to be linked to the condition.

But it's clear environmental factors play a role in determining whether you'll experience allergies, as well. In the United States, rates of all sorts of allergies have been increasing in recent years, especially in children. Many scientists blame this on something called the hygiene hypothesis — the idea that growing up in an overly clean, sterilized environment somehow messes with the natural development of the immune system, making it more prone to errors, like mistaking a harmless pollen grain for an invader.

3) Can I develop seasonal allergies over time? And can they go away?

Yes and yes.

Most people with seasonal allergies develop them some time after reaching adulthood, and these allergies can change unpredictably — in some cases, disappearing one spring after years of suffering. But scientists still really have no idea how or why this happens. Claims that you can eliminate seasonal allergies by changing your diet are unsubstantiated.

4) How can I figure out if I have seasonal allergies?

The easiest way is to consider your symptoms.

Seasonal allergies share some symptoms with the common cold (fatigue, sneezing, a runny nose, and nasal congestion), but there are a few key differences.

If you're experiencing body aches and pains or a fever, and if your symptoms last for only a week or two, you probably have a cold. If you have longer-term symptoms (lasting four to six weeks) and they include itchy eyes, you probably have a seasonal allergy.

You can also go to an allergist and take a test. For the most common kind, a doctor will prick your skin with extracts made from many different kinds of allergens, including common pollens. If you develop inflammation around the site of one of the pricks, it indicates you're allergic to it.

Generic antihistamines work just as well as name brands.

5) What should I do to make my allergies less awful?

If you're unsure whether you actually have allergies, it's probably a good idea to see a doctor before taking any new medications.

If you know you suffer from seasonal allergies, the first thing to do is try an over-the-counter antihistamine. By limiting the activity of histamine in your body, it can reduce itchiness, watery eyes, and a runny nose, though it probably won't make you feel absolutely perfect.

This interactive tool from Iodine can help you find a good medication for your symptoms. Although early antihistamines (like Benadryl) had the side effect of drowsiness, more recent ones (like Claritin and Allegra) do not. Consumer Reports recommends generic versions of Claritin (called loratadine) or Zyrtec (called cetirizine), because they're the exact same drug as the name brand versions and are generally much cheaper.

If you're still suffering despite help from antihistamines, try limiting your exposure to pollen. Pollen season varies by location, and different plants release their pollen at different times, but trees generally pollinate in the spring and grasses in the summer. Pollen counts forecast the amount of pollen in the air for your area on a given day (the number indicates the amount of individual grains in a cubic meter of air), so you can avoid spending time outside on particularly high-pollen days (they tend to be windy and dry). The Mayo Clinic has a bunch of other tips for minimizing exposure.

If your symptoms are really severe — and if you also have asthma, which can be aggravated by seasonal allergies — you might want to see an allergist and ask for allergy shots. These work by deliberately introducing an extract made from pollen into your body to make it less sensitive. The shots can be effective but are expensive, can cause side effects, and involve weekly or monthly shots for years at a time.


6) How is this related to food allergies and other sorts of allergies?

The mechanism (your overzealous immune system) is the same, but the symptoms can be quite different: someone allergic to peanuts, for instance, can experience anaphylactic shock, which involves rapid throat swelling and can even lead to death. Because they're connected, in some people, an onset of seasonal allergies can make food allergies worse.

7) Is there anything else I should know about seasonal allergies?

Yes. Scientists have recently determined that because of climate change, pollen season is likely to become longer and feature even higher amounts of pollen than it does currently. Right now in the US, it generally starts in mid-April and peaks in early May; by 2020, it'll begin in mid-March, peak in April, and continue even later into the summer, with higher amounts of pollen in the air at any given time.

Happy sneezing.

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