There are so many reasons you might have woken up with puffy eyes. Maybe you slept poorly; maybe you slept poorly because you were drunk. Perhaps you were drunk and got punched in the eye. Suddenly realizing that pollen allergies are to blame for your swollen sockets might seem a bit anticlimactic, but rest assured they’re the result of a very exciting immune system bar fight inside your face.

Every spring, horny trees release pollen into the air in an attempt to mate. Unfortunately, as those golden specks, carrying the tree’s reproductive material, travel through the air to touch those of another tree’s private parts, they sometimes wind up in our nostrils and mouths instead. Our immune systems, being extremely xenophobic, kick into overdrive to force the innocent invaders out.

The result is inflammation, which everyone is well acquainted with. What’s not as obvious is the reason inflammation is such an integral part of the immune response in the first place.

When pollen gets into your bloodstream, white blood cells patrolling the body’s premises immediately identify it as an invader, prompting the release of antibodies called immunoglobulins, or IgE. These beckon to the other cells of the immune system, which respond by pumping out chemicals, like histamine, that kickstart the inflammatory response. Unfortunately, this strategy is rather blunt. Swelling, caused by a rush of blood into the areas where invaders collect, “helps isolate the foreign substance from further contact with body tissues,” as the U.S. National Library of Medicine puts it. It’s kind of like Lebron James taking up as much space as possible to box out an opponent trying to grab the ball.

Because pollen primarily invades the body through the mucous membranes — the wet ones — those organs are where the majority of inflammation happens. Your eyeballs, slick and uncovered, are especially vulnerable, as is the lining of the nostrils and lungs. In addition to causing swelling, the cocktail of chemicals associated with the inflammatory response makes the affected organs water, itch, hurt, and turn red. That’s why your eyes feel terrible and you’re constantly sneezing and wiping your nose. If you find yourself wailing Why?, remember: Your body’s just trying to keep you safe.

Of course, overzealous protection can get annoying, which is why antihistamines like Zyrtec and Benadryl exist. True to their class name, they block histamine from carrying out its inflammation-triggering effects. As Inverse previously reported:

Benadryl’s main ingredient is classified as an “inverse agonist of the histamine H1 receptor,” which is a complicated way of saying its job is to box histamine out of its slot on the receptor, preventing it from kicking off the inflammation process altogether. Taking an anti-allergy pill floods your bloodstream with diphenhydramine molecules, which prevent histamine from binding. Rapid relief ensues, allowing your hot, swollen body to return to its normal size.

If it seems like pollen is making your eyes redder and itchier than usual, it might be because pollen production and release is generally increasing. Some immunologists have speculated that pollen allergies are getting worse because different species of trees, confused by a changing climate, now tend to release all their pollen at once, rather than in a staggered order. It doesn’t help that climate change has caused more carbon dioxide to pool in the atmosphere, prompting trees to make up to four times more pollen. Unfortunately, if you suffer from seasonal allergies, there’s no guarantee they’ll get any less intense. Eye drops, anyone?