Allergic? This is how your body reacts to pollen

Allergies can be a painful experience, causing watery eyes, aching sinuses, and a persistently runny or blocked nose. The culprit can vary, from trees to grasses releasing pollen into the air, but the body's reaction mechanism remains the same.

For many, the first allergic attack may seem to come out of nowhere. Each spring, as the air fills with pollen, these tiny grains get trapped in the mucous membranes of the eyes, nose, and throat. For a time, sometimes years, the body may not react noticeably. However, in some individuals, an allergic reaction builds up slowly.

The immune system works quietly, sending out scout cells called dendritic cells to capture parts of potential invaders for analysis. Researchers are still exploring why, but at some point, the immune system in some people begins to treat these innocent pollen grains as if they were a parasitic worm. This misidentification prompts the immune system to release chemical messengers known as cytokines. These cytokines drive inflammation and activate white blood cells, which in turn produce antibodies.

These antibodies are then placed on mast cells, acting like small landmines in the eyes, nose, and airways, preparing the body for the next pollen assault. This process is called sensitization, where the immune system learns to recognize pollen as a threat and gears up for future attacks. The body becomes hypersensitive, or allergic. Some people develop allergies and hypersensitivity after a single exposure to pollen, while others develop it after several allergy seasons. Some become hypersensitive as children. Moving to a new location and encountering new types of pollen can also trigger it. Sometimes, a particularly difficult pollen season is enough to activate the immune system's defense mechanisms.

Most allergies follow a similar pattern: the immune system learns to perceive something as a threat and then reacts when it reappears. The next time pollen arrives, it can bind to the antibodies the body has deployed, triggering the mast cells in the eyes, nose, and airways. The result is a surge of inflammatory substances, including histamine. Histamine causes plasma and immune cells to exit nearby blood vessels. While this would help the body fight a parasite, with pollen, it only leads to redness and swollen eyes. All inflammatory substances also cause the body to produce excess mucus to trap the grains, resulting in a runny nose and cough. Histamine also irritates nerve endings, causing itching. As a result, eyes water.