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An allergic reaction is your body's response to a perceived invader, called an allergen.
You breathe in, eat or touch potential allergens all the time, mostly without even taking notice. That's because they're usually harmless. But if your immune system mistakes pollen, pet dander or some other safe substance for a dangerous invader, you may develop an allergy.
You initially become allergic — or sensitized — to a substance before any symptoms appear. But behind the scenes, your immune system is in high gear.
Most allergies develop in the same way. Let's say you've just inhaled ragweed pollen. The first time, you might not even sneeze.
But when the allergen reaches your nasal lining, immune cells called macrophages swiftly move in. Macrophages swallow up allergen particles, and then hook up with certain toxin-fighting white blood cells. Once alerted, other white cells produce a protein called IgE, in this case, programmed to react to ragweed pollen.
Allergen-specific IgE antibodies then attach to mast cells in the mucous membranes of your eyes, nose and throat. You also have mast cells in your digestive tract and skin. These cells are storehouses for allergy-symptom-causing chemicals, including histamine, which is responsible for telltale allergic itching and swelling.
All of this happens the first time you encounter an allergen. After you're sensitized, you'll have allergy symptoms whenever you're exposed to the substance, whether it's something you inhale, swallow or get on your skin.
In this case, the next time you encounter ragweed pollen, the allergen latches on to IgE dotting the surface of mast cells in your upper respiratory tract. Each allergen particle fits neatly between two IgE proteins, creating linked pairs. This linkage makes the mast cell break open, releasing histamine and other chemicals.
Your eyes itch and water, and your nose and throat swell and secrete mucus — a classic allergy attack is under way.
Many inhaled allergens and some allergens in food can also affect mast cells in your lower respiratory system, causing asthma. Other allergens, such as nickel and latex, trigger histamine release from mast cells in your skin, resulting in allergic rashes or dermatitis. |