Understanding Allergy and Asthma
According to the World Health Organization, allergies are the most widespread chronic condition in the world. There is no question that allergies are a major problem in this country. They are so prevalent that they affect almost every household. A great number of Americans either have allergies or know someone who does. In the United States alone, it is estimated that the number of people who suffer from allergies in one form or another may be as high as 50 percent,1 costing them billions of dollars annually. And some doctors say these figures may be low estimates.
What Is an Allergy?
An allergy is a hypersensitivity or abnormal reaction to something that is ordinarily harmless to most people. Allergic reactions are caused by malfunctions of the immune system, the complex defense system that protects our bodies against invasion by bacteria, viruses, parasites, and other foreign substances or organisms that threaten our health. A multitude of common, otherwise harmless substances can trigger the susceptible immune system to overreact and produce a variety of allergic symptoms depending on the part of the body that is affected.
Allergies can be inherited; if your parents or grandparents have a history of allergic sensitivities, you may develop allergy symptoms. If one parent has allergies, a child has a 20-40 percent chance of developing sensitivities; if both parents are allergic, a 40-60 percent chance. However, even though allergies can run in families, you can inherit just the tendency to be allergic, but not necessarily the same sensitivities that bother your parents. Allergies can also be influenced by a host of factors or conditions, such as geographical location, the time of the year, the climate and humidity, the pets you keep, the furnishings of your home or apartment, your housekeeping habits, what you eat or drink, the products you use, the drugs and medications you take, exercise, indoor and outdoor contaminants, and even your job.
Some allergies occur only at certain times of the year, while others are present all the time. Seasonal allergies coincide with the seasons when trees, grasses, and weeds begin to pollinate. The duration of the season depends on geographic location. Perennial, or year-round, allergies are usually caused by something you come into contact with every day of your life, including animal allergens, mold, and the droppings of dust mites and cockroaches. Since it is possible to be allergic to more than one allergen, many people suffer from both seasonal and perennial allergies.
When Do Allergies Begin?
Allergies usually appear before twenty years of age, and there is a tendency for them to start during early childhood. Young boys are more likely to suffer from allergies than young girls, but the pattern reverses itself in adulthood to affect women more than men. Allergies may change, they may come and go with no regularity, symptoms may wax or wane in intensity, or shift from one part of the body to another as a person progresses through different life stages, but the tendency to be allergic seldom goes away. Many individuals improve as years go on, but some do not.
The Immune System
In her book What's in the Air?
, Dr. Gillian Shepherd, clinical associate professor of medicine at Weill Medical College of Cornell University, has a most appropriate description for the human immune system. She calls it our body's "homeland defense system" and likens it to a giant network, similar to a road map showing many different routes, one of which leads to allergies.
Every minute of every day, a myriad of foreign invaders enter our bodies with no detrimental effects. Any foreign substance that causes the immune system to react is called an allergen (doctors also call these "antigens"). Allergens can be taken into our bodies in several different ways: via airborne substances we inhale; by food or drugs we ingest; by vaccines, medicines, and insect stings injected into our bodies; and through substances that come into contact with our skin.
Normally, when an allergen enters the body, the immune system springs into action and produces specifically programmed antibodies known as immunoglobulins
to attack and destroy it. There are five different groups of immunoglobulins: IgA, IgD, IgE, IgG, and IgM. Each plays a different role that contributes to the functioning of the immune system. Immunoglobulin E, or IgE, is the antibody responsible for allergic reactions.
Along with IgE, three other types of body cells play a prime role in allergic reactions: mast cells
, found in the tissues throughout the body (primarily in the mucous membranes of the respiratory and gastrointestinal tracts) and in the skin; basophils
, a type of white cell (or leukocyte) found in the blood; and eosinophils
, other special white blood cells.
The Basics of an Allergic Attack
In an allergic person, the immune system learns to respond to one or more innocent foreign substances as if it or they were dangerous to the body. In the case of pets, for instance, the immune system perceives their dander, sebaceous gland, and salivary and urinary extracts as threats. Pet allergens are usually considered airborne allergens (though rashes caused by pet licking and contact dermatitis from pet dander are examples of non-airborne allergic reactions). Along with other inhaled substances such as pollens, mold spores, and the droppings of dust mites and cockroaches, they enter the body via the nose, throat, and lungs. Breathing them in can affect your entire respiratory tract. "For allergens to become capable of being inhaled, they have to be tiny--1 to 5 microns," Dr. Shepherd says. "This means they are a millionth of a meter, or many times smaller than the dot at the end of this sentence."
The first step in the development of an allergic reaction is exposure to an allergen. Suppose, for instance, you have the potential to be allergic to cats. The protein cats produce that causes allergies in humans is called Fel d 1. Studies indicate that the sebaceous glands at the hair roots and the salivary glands are the most potent cat allergen sites. If you are a person destined to be sensitized to cats, when the tiny Fel d 1 protein comes in contact with your nose, lungs, eyes, or skin, your immune system reacts by producing specific IgE antibodies to this foreign substance.
Your initial exposure to the Fel d 1 cat allergen causes the IgE antibodies to bind in great number on the mast cells and basophils--many thousands may collect on a single cell--but you probably won't experience any symptoms. An allergen does not provoke a reaction the first time you encounter it.
The immune system is simply gearing up to defend itself against future invasions by that same allergen. At this point, however, you are sensitized
Sensitization, or the process that leads to development of symptoms in persons intolerant to a particular allergen, requires exposure over a period of time--anywhere from hours, days, months, or years--to develop. Consequently, the second time your body encounters cat allergen (or maybe the tenth time, or the fiftieth time, or even the hundredth time) a sequence of biochemical reactions will occur culminating in the classic symptoms associated with airborne allergies.
When that occurs, and the Fel d 1 comes into contact with the IgE antibody that is produced to react against it, the mast cells and basophils attack the intruder and release a flood of destructive chemicals (the most important being histamine) into the surrounding tissues and bloodstream to trigger inflammation, either locally or systemically.
The union of an allergen and the IgE that takes place on the surface of the two cells is explosive. Several authors, in fact, have likened what happens to an explosion, comparing mast cells and basophils to grenades or land mines, and the IgE antibodies that bind to them to detonators.
Depending on the tissue in which the "explosion" occurs, the allergic response differs. If the reaction to Fel d 1 occurs in the nose and throat, the responses can cause immediate swelling, itchiness, sneezing, a runny discharge, nasal congestion, an itchy or scratchy sore throat, and more. A similar reaction occurs in the lining of the eyes causing tearing, intense itching, and swelling. In the lungs, the muscles surrounding the air passages contract to make breathing more difficult, possibly starting the symptoms of asthma. If the reaction occurred from touching the cat, local swelling of the skin, itchiness, hives, or rashes may result.
This is not the end of the scenario, however. A few hours after the initial attack, in what is called the "late-phase reaction," eosinophils and additional basophils accumulate at the allergy site and release a host of inflammatory chemicals that contribute to both the severity of symptoms and the persistence of the attack.
The Cumulative or "Rain Barrel" Effect
Allergies are cumulative. In other words, they build up, and people can have varying sensitivities to different allergens. Every allergic person's immune system has a tolerance level above which symptoms will develop. This is often referred to as the "rain barrel" effect. Basically, when an allergic person's rain barrel is empty or partially filled, there are no allergic symptoms. However, when a combination of allergens, infection, and stress pile up, the rain barrel can fill up and overflow.
Someone who is allergic to a pet, for instance, may have no noticeable symptoms when the total exposure is below his or her tolerance level (the amount of substance or substances needed to provoke a reaction). That person may also have varying degrees of sensitivities to other substances found in and around his environment, such as dust, mold spores, pollens, soaps, cosmetics, and the like.
If a surplus of these allergens...