Mast cells, part of the cast of characters in the immune system, are the ringleaders of hypersensitivity reactions. Ordinarily they are peace loving. But when tissues are flooded with irritating compounds, mast cells become trigger-happy troublemakers, unable to distinguish friend from foe.
A grain of pollen comes along; the mast cell sees it as life threatening, melts down, and spews histamine everywhere. Tender tissues in the throat, nose, and sinuses become hot and swollen. Abundant mucus is produced as a defense. Eyes become red and itchy.
It wouldn’t be so bad if just a few mast cells were acting up. However, if they’re repeatedly triggered by pollen, food, or animal dander, they multiply by a factor of up to 10. When these specialized immune cells in your respiratory linings are triggered by pollen to release histamines, it spells trouble for your sinuses.