Scientists have a pretty good understanding of what happens inside the body during an allergic reaction.
Three players are involved:
The first are allergens. An allergen is a normally harmless substance that, for some reason, a person with allergies reacts to.
The second are immune cells. These cells help protect a person from harmful invaders.
The third are natural chemicals released by the immune cells.
The specific symptoms of an allergic reaction will depend on the allergen, how allergic the person is to it, and where it enters the body. Symptoms can either affect the whole body or just one particular area.
When an airborne allergen, like pollen, enters the nose of a person with allergies, their immune system reacts. Some cells will react very quickly; others will take a little longer.
The first set of immune cells converge on the area where the allergen is. They recognize the allergen and become activated. This causes the release of a number of chemicals.
One of the chemicals released is histamine. Histamine affects the surrounding tissue, blood vessels, and nerves. This immediately causes symptoms, including sneezing and a runny nose. Another symptom, nasal congestion, can take a few minutes to begin.
The early immune response also alerts the immune system to send in other cells. Several hours later, these cells enter the area, become activated, and release their chemicals. Most of these chemicals are the same ones released in the early response. They also cause inflammation, swelling, and congestion within the affected areas.
The nose is the most common area affected by allergens found in this air. This means that sneezing, and a runny, stuffy, and/or itchy nose are quite common. The eyes may also be affected by this type of allergy, causing:
• Red, itchy, watery eyes
• Swelling in the whites of the eyes
• A feeling of grittiness in the eyes, and
• Swelling and blueness of the skin below the eyes, or allergic shiners.
And a person's ears and throat can also be affected. Symptoms can include:
• Itchy throat, sore throat, or horse voice
• Itchy ears, congestion or popping of the ears