Normally, your immune system helps protect you. It does this by sending in special cells, that attack whenever viruses, bacteria, or other harmful substances invade your body. This response helps neutralize the foreign invaders.
But many things enter your body that the immune system usually views as harmless. This can include things like pet hair; dust mites; and tree, weed, or grass pollen.
In a person with allergies, the immune system mistakes these harmless substances, known as allergens, for a potential threat.
The first time the immune system sees an allergen, it reacts by activating special cells. These cells make large amounts of proteins, called antibodies, that are specific to the type of allergen. These antib odies then attach to other immune cells, making them sensitive to the specific allergen.
The next time the allergen enters the body, these sensitive immune cells quickly attack. They attach to the allergen, which causes a release of natural chemicals, including histamine. These chemicals enter the surrounding tissue and cause many of the early symptoms of allergies.
For a person with allergic rhinitis, which affects the nose and eyes, sneezing; an itchy, runny nose; and red, itchy, watery eyes can result.
Two to four hours later, another response begins as more immune cells become activated and release their chemicals. These chemicals cause inflammation, swelling, and congestion within the affected areas.