Why Does Pollen Cause Allergic Reactions?

Seasonal AllergiesPollen is everywhere, whether we can see it or not. In the spring, you might find a dusting of tiny pollen grains on your car when you leave for work in the morning. On days with especially high pollen counts, you might even notice a murky yellow haze rising above fields of grasses and wildflowers. But if pollen is so common, why does it cause allergic reactions in roughly 20 percent of all Americans?

In fact, there are two different types of pollen, only one of which causes seasonal allergies.

Entomophilous pollen is the heavy, sticky pollen that’s dispersed by bees and other insect pollinators. Anemophilous pollen, on the other hand, is light enough to be dispersed in large quantities by wind alone. It’s this type of pollen that typically causes allergic reactions in humans.

As you can see in this illustration, each grain of pollen is surrounded by a spiky outer shell that protects the reproductive sperm nuclei hidden inside.

As the pollen grains are dispersed on the breeze, these spikes make it easy for them to adhere to surfaces, including our clothes and bodies. On days with high concentrations of pollen in the air, we’ll inevitably inhale some of these grains into our nose and mouth. When this happens, our immune systems can sometimes mistake the harmless pollen grains for potentially-dangerous foreign bodies, releasing antibodies to find off the invaders. This, in turn, triggers the release of a chemical called histamine which causes familiar allergy symptoms such as runny nose, watery eyes and inflammation.

In essence, these allergies are caused by an overzealous immune response to pollen exposure.

There’s still some debate in the scientific community, however, as to why pollen allergies are as common as they are. If humans have been regularly exposed to pollen every year for hundreds of thousands of years, shouldn’t our immune systems be able to distinguish pollen grains from real threats by now?

One theory suggests that pollen allergies arise when people are exposed to pollen while fighting off a virus such as the common cold. In this scenario, the immune system might falsely associate pollen grains with the viral infection, causing an allergy to develop. Another theory suggests that some people may simply have a genetic predisposition to seasonal allergies that’s passed down from the immune systems of their ancestors.

Fortunately, we now have access to over-the-counter drugs like antihistamines that make this time of year a little more bearable for allergy sufferers. To learn more about all the marvels and mysteries of the human body, stay tuned for the latest updates from my blog!