About 50 million Americans have allergies, according to the Asthma and Allergy Foundation of America. The sneezing, coughing, itchy eyes, runny nose and scratchy throat associated with allergies affect one in three Americans. Allergies are the fifth most common disease among adults and the third most common childhood condition, as of publication. Indoor and outdoor allergies including hay fever, reactions to cat dander and allergies related to trees, mold, skin or food could make life difficult for those who develop allergies.
Genetic Component
You have a higher risk for developing allergies if one or both of your parents had allergies. If one parent has allergies, chances are one in three that each of that parent's children also will have allergies. If both parents have allergic reactions, risks increase to seven out of 10. While genetics increases your risk for allergies, your body’s overreaction causes allergies to develop.
First Exposure
Your first exposure to a particular substance does not cause an allergic reaction to that material, but the initial exposure starts a chain of events that leads to allergic reaction. For example, the first time your nose is exposed to cat dandruff, you may be able to pet the cat and stir up its dandruff without experiencing unpleasant symptoms. Small dandruff particles may enter your nose and encounter mucus membranes lining your nasal cavity. The membranes regularly produce mucus to flush away dirt and debris.
IgE
Invading particles are carried to the lymph nodes, where they encounter lymphocytes, white blood cells that react by producing the primary antibody immunoglobulin E, or IgE. The IgE, now sensitized to cat dander, attaches itself to mast cells throughout your body. The mast cells, and the attached antibodies, can become vigilant against cat dander and could launch an allergic reaction the next time you encounter a cat. There are high numbers of mast cells in your nose, lungs, skin and gastrointestinal tract, according to Allegro Healthcare.
Second Exposure
The second exposure to an allergen -- the substance that causes a response -- elicits an allergic reaction. The allergen enters the body through the mucus membranes and encounters the mast cells and the attached antibodies. The allergen then bonds with the IgE. The mast cells degranulate, or break up, and degranulated mast cells release chemical messengers -- or mediators -- that include histamines. These mediators circulate in your body and trigger symptoms of an allergic reaction like itching, watery eyes, hives or gastrointestinal upset.
