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Why Do Allergies Make You Sneeze?

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 Biology   |   Environmental   |   Science
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Do you suffer from allergies? Follow the dendritic cell and the entire Scientific American Allergy Orchestra to discover how allergens from pollen to pet dander can change the body’s tune.

Transcript:

Sneezy? Itchy? Perhaps your seasonal allergies have your immune system playing the wrong tune. Your immune system is like an assembly of musicians, each with a job to do.

The dendritic cell—here played by the conductor—orchestrates a response to protect the body from invaders. Bacteria lurking? The conductor leads the anti-bacterial response. Virus? New sheet music, new program.

Unlike a bacterium or virus that could harm the body, an allergen is a harmless substance that fools the immune system into mounting an inappropriate response. The first time an allergen enters your body, a B cell—here played by a guitarist—reacts as if it is harmful. It secretes an immunoglobulin protein, IgE, which acts like sheet music.

This provides a program for future reference. IgE “music” is handed out to MAST CELLS in the lungs, intestinal tract, and nose. This music just sits on the stands. If the allergen never shows up again, nothing will happen. But if an allergen sneaks in, finds its matching IgE, and activates a mast cell…

The mast cell erupts.

Histamine and other chemicals flood the body, triggering a cascade of effects. They recruit other cells and chemicals to get involved in the same program. Cacophony. Blood vessels dilate and tissue swell. Mucus production ramps up and muscles contract, which can lead to a wet, tightened airway.

Not every allergic reaction causes a full meltdown. Sometimes the allergen only affects the mast cells in one section, like the common eye-watering reaction to tree pollen. But in rare cases, given the right conditions, an allergic reaction can kill you.

Why do some people’s immune systems overreact to harmless substances? Scientists think the timing of the first exposure may be key. Babies exposed to pet dander when they are less than six months old tend not to be allergic to those pets. Another part is coded in your DNA. If you find your immune system out of tune, doctors who specialize in treatment have all kinds of strategies to help bring your body back into harmony.

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