To someone with allergies, the tiniest thing can cause the biggest trouble. A seemingly harmless bit of dust, dander from a cat, or a puff of pollen floating in the air can lead to allergy symptoms.
Ever wonder why the human body reacts the way it does? Why do we sneeze? Why do our noses run and our eyes tear up? Basically, an allergy is the body's over-eager reaction to a misinterpreted threat, something that is normally harmless. When exposed to an allergen, the body responds by trying to block it out. In some people, these harmless substances can trigger an immune response in the body to help rescue the body from these "invaders." The body produces an antibody called IgE (immunoglobulin E), which attaches to cells called mast cells. This causes the release of various substances, including histamine, which cause allergy symptoms.
It's good to know that your immune system works so hard to protect you, but for those with seasonal or year-round allergies, this defence usually leads to inflammation. It's the inflammatory response that causes that congested feeling and the need to sneeze. Your eyes may go on the defensive, too; tears may form and blood vessels may swell and give you that puffy, red-eyed look.