Allergies are a short-term inflammation of the mucous membranes that line the nasal passages. "Hay fever," as the condition is commonly called, is caused by airborne pollens from trees, grasses, flowers, and weeds. Allergy season typically kicks off in the spring and fall when certain trees or grasses pollinate. When pollen season starts and how long it lasts varies throughout the country. In southern states, trees can start pollinating as early as late February and grass can start by the end of April, while in midwestern states allergies may not flare up until May. Another round of allergies may begin in late summer or early fall when ragweed is the culprit. In western states, grass pollinates for a longer period of time and certain weeds exist that can keep allergies blooming into the fall.
Allergies caused by pollen and other allergens affect 40 million Americans and cost more than $1 billion in annual treatment costs. Although it's usually not a dangerous condition, it can be very uncomfortable and, for some people, can severely disrupt daily activities. The standard reactions include sneezing, itchy throat, headache, swollen sinuses, runny nose, and itchy, watery eyes, .
In allergies, airborne pollen from various seasonal plants—or, in some cases, spores from mold—enter the body through the eyes, nose, or throat, and trigger an allergic reaction. Normally, the immune system does not respond to mild substances like pollen and mold. But in sensitive individuals, the body's defense mechanism views these allergens as it would an infectious agent and mounts an attack. Once the immune system has detected the "invader," it unleashes a cascade of chemicals such as histamine and other compounds resulting in localized inflammation that leads to irritation and discomfort. The symptoms of allergic reaction begin 5 to 10 minutes after allergen exposure, subside within an hour, and may return two to four hours later.
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