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As a retired Registered Nurse, I'm often asked questions just like this about allergy information. People want to know what makes them different from their friends who can enjoy the outdoors, pet their cats, and dust their house without a sniffle.
Allergies tend to be genetic, running in families. Interestingly though, family members are not always allergic to the same things. Their allergies may not always affect them the same way. Dad may be allergic to almost all the pollens, sister allergic to several foods, grasses and animals, and little brother allergic to mold and ragweed. Mom and big brother may have no allergies at all. One family member may have hives or skin allergies, another asthma, and another hay fever. Or they may have any combination of these three.
"A family history of allergies is the single most important factor that predisposes a person to develop allergic disease. If one parent has allergic disease, the estimated risk of the child to develop allergies is 48%; the child's risk grows to 70% if both parents have allergies."
Exposure to new allergens can also bring on allergic symptoms. It's very common for me to hear people say, "I didn't have any allergies at all until I moved here." They may be referring to a move from another area of the country where there are different pollens present, or just a move across town, perhaps to a home with different environmental allergens present. Either way, these people probably already had a genetic tendency toward allergies, often called "atopy" or being "atopic" by those in the medical field. Sometimes atopy is associated with an "allergic triad", which is:
What this means is that the person who has this genetic tendency toward hypersensitivity is more likely to develop asthma, allergic skin conditions, or allergic rhinitis. There seems to be an association between these three diseases. The person who experiences one of them is more likely to suffer from one or both of the others at some time in their life. Atopic people are more susceptible to developing an overreactive immune system. The immune system is the part of our body that fights bacteria, viruses, and anything else it recognizes as foreign. But it becomes hypersensitive when it begins to see normal substances as intruders.
Our bodies are a fascinating handiwork. We are created in such a way that every part coordinates in minute precision with every other part.
For example, on the surfaces of some cells there are tiny areas that require powerful microscopes to explore. These areas are receptors for antibodies. As you might know, antibodies are cells that ward off infection, viruses, and other threats. Antibodies are highly specialized. Each has it's own specific assignment. Some are responsible to fight a certain virus, others to fight a specific bacteria. Antibodies are also called immunoglobulins. Immunoglobulin E (IgE) is the antibody commonly associated with allergies.
"Each type of IgE has specific 'radar' for one type of allergen only. That's why some people are only allergic to cat dander (they only have the IgE antibodies specific to cat dander) and others seem to be allergic to everything (they have many more types of IgE antibodies.)"
-- From www.AAAAI.org
Receptor cells for IgE are located in various parts of the body, including areas near the eyes, ears, sinuses, throat, lungs, skin, and gastrointestinal tract. These receptor cells are called mast cells. Other cells with receptors for IgE are in the blood stream. They are called basophils. A few other cells have receptors for IgE also, but mast cells and basophils are the most prominent ones.
The problem for allergy sufferers occurs when the body becomes confused about substances such as pollen, dust mites, cat dander, common molds, foods or medications. Each of these substances can be recognized as an intruder, and the body begins creating IgE antibodies toward it. But it is not usually able to get the mature IgE in place soon enough to do much damage in the first round.
However, the body has a fantastic memory! It never forgets that challenge to it's integrity. The next time the immune system is exposed to that allergy information or allergen, such as cat dander, it rapidly produces IgE cat dander antibodies. As these IgE antibodies are produced, a complicated chain of microscopic events takes place within just a few minutes. This results in presentation of the IgE antibody to the mast cells in the tissues surrounding the eyes, sinuses, nose, and lungs, and to basophils in the blood stream. The receptors on mast cells have a high affinity or liking for IgE antibodies. The union of IgE antibodies with mast cells enables the allergen to cross-link between two of the antibodies. As allergens begin to rapidly cross-link with more IgE on the receptor sites of the mast cell, the mast cell releases powerful chemicals such as histamines and leukotrienes, both of which mediate (or bring on) inflammation.
Inflammation is not always bad. Inflammation causes the blood vessels in the skin to dilate, allowing blood to rush in, bringing antibodies to fight the infection or intruder. As the blood rushes to the area, fluid containing antibodies is leaked into the surrounding tissues from the blood, and the tissues become swollen. Antibodies in this swollen area are working hard to fight infection.
But for the allergy sufferer, this inflammatory process is not needed, because there is no real intruder to fight. The inflammation in the allergic response releases chemicals that can cause itching in the eyes and skin and congestion in the sinuses and lungs. This results in swelling and increased mucous production which can obstruct breathing and cause a runny nose and itchy, watery eyes. In some cases hives may occur as fluid seeps into the outer layers of skin. Each time the allergy sufferer is exposed to the allergen, another series of these microscopic processes occurs. As long as there is exposure to the allergen, there seems to be no end to the inflammatory response.
It's also important to note that hours after recovery from the initial allergic reaction, a second or late phase reaction may occur. In the late phase, the receptor cells in the blood (basophils) influence other blood cells called eosinophils to release more mediators of inflammation. Enzymes are released during this late phase, some of which can cause permanent tissue damage if allowed to continue over time. This is especially serious for asthmatics because it can lead to what doctors call "airway remodeling." The lungs are remodeled by replacing healthy tissue with scar tissue. For additional information on this late phase response, see the section titled "Early and late phase reactions" on the following page: http://www.worldallergy.org/professional/allergic_diseases_center/ige/. You may also be interested in viewing the video included in that section.
"Eosinophils also play prominent roles in late-phase reactions that affect some people with allergies and asthma, particularly with symptoms of nasal congestion that can occur hours after an initial episode of allergic rhinitis. If you have uncontrolled asthma, constant eosinophil activity may lead to airway remodeling - the replacement of healthy tissue with scar tissue - and can potentially cause irreversible loss of lung function. Preventing this type of serious lung damage is one of the main goals of treating asthma early and aggressively..."
-- From Allergies and Asthma For Dummies by William E. Berger, M.D.
This information is for educational purposes only. Always consult with your doctor first about your specific condition, treatment options and other health concerns you may have.