Tips to Remember: What is an allergic reaction?
Approximately 50 million Americans suffer from some form of allergic disease, and the
incidence is increasing. When most of us think of allergies, we think of sneezing, a runny nose
or watery eyes. While those are symptoms of some types of allergic disease, an allergic
reaction is actually a product of several events occurring within your immune system.
The immune system
The immune system serves as the body's defense mechanism against the countless different
substances present in the air we breathe, the foods we eat, and the things we touch. Within this
immense group of materials, the term “allergen” refers to any substance that can trigger an
allergic response. Common allergens include pollen, mold, animal dander, and cockroach and
house dust mite droppings.
Antibodies circulate in the bloodstream and are present in almost all bodily fluids. They help to
capture unwanted invaders. People who have allergies have an antibody called Immunoglobulin
E, or IgE. When allergens first enter the body of a person predisposed to allergies, a series of
reactions occurs and allergen-specific IgE antibodies are produced. Following IgE production,
these antibodies travel to cells called mast cells, which are particularly plentiful in the nose, eyes,
lungs and gastrointestinal tract. The IgE antibodies attach themselves to the surface of the mast
cells and wait for their particular allergen.
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.)
The next time an allergic individual comes into contact with the allergens to which he or she is
sensitive, the allergens will be captured by the IgE. This initiates the release of chemical
“mediators” such as histamine and other chemicals from the mast cells. These mediators produce
the symptoms of an allergic reaction, such as swelling of tissues, sneezing, wheezing, coughing
and other reactions.
The allergic reaction typically continues: these newly released mediators recruit other
inflammatory cells to that site, resulting in additional inflammation. Many symptoms of chronic
allergic disease—such as swelling, excessive mucus and hyperresponsiveness to irritating
stimuli—are the result of tissue inflammation due to ongoing exposure to allergens.
It is not yet fully understood why some substances trigger allergies and others do not, nor why
every person does not develop an allergic reaction after exposure to allergens. 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.
Types of allergic disease
The existence of IgE antibodies is common to all forms of allergic disease. But the physical
symptoms differ depending on the type of mediator released and where they act. When a person
with allergies begins to experience symptoms, key questions are: What allergens am I reacting
to? When, and how much, am I exposed to these substances?
Major allergic diseases include:
Allergic rhinitis, or “hay fever”
Allergic conjunctivitis (an eye reaction)
Asthma
Atopic dermatitis, or allergic skin reactions
Urticaria, also known as hives
Severe allergic reactions to substances such as food, latex, medications, and insect
stings
Problems commonly resulting from allergic rhinitis—sinusitis and otitis media (ear
infections)
Symptoms of allergic rhinitis, commonly referred to as “hay fever,” occur when allergens touch
the lining of the nose—called the mucus membranes—of a person who is sensitive to that
particular allergen. Allergic rhinitis is characterized by congestion, itching and dripping of the nose
and itchy, watery eyes. If the person continues to have daily, ongoing exposure to the responsible
allergen(s), the symptoms will continue. Similar to allergic rhinitis, allergic conjunctivitis occurs
when the eyes react to allergens with symptoms of reddening, itching and swelling.
Symptoms of atopic dermatitis, also called eczema, often result from allergen exposure to the
skin. Dermatitis symptoms include itching, reddening, and flaking or peeling of the skin.
Symptoms begin in childhood for 80% of those with atopic dermatitis. Dermatitis often precedes
other allergic disorders; over 50% of those with atopic dermatitis also develop asthma.
Urticaria, or hives, another allergic skin reaction, is characterized by itchy red bumps that can
occur in clumps and be either large or small. Hives are often triggered by infection, certain foods
or medications. Foods commonly associated with hives include nuts, tomatoes, shellfish and
berries. Medications include penicillin, sulfa, anti-seizure medications, phenobarbital and aspirin.
Asthma is a chronic lung disease that affects more than 17 million Americans and is
characterized by coughing, chest tightness, shortness of breath and wheezing. Allergic rhinitis is
considered a risk factor in developing asthma: up to 78% of those with asthma also have allergic
rhinitis.
When an individual experiences asthma symptoms, the inflamed airways become constricted so
it becomes more difficult to breathe through the narrowed air passages. For people with allergies,
inhaling allergens may produce increased inflammation of the airway lining and further narrowing
of the air passages. Asthma may also occur as a result of other stimuli, such as respiratory tract
infections or exposure to irritants.
Individuals who have allergies to specific foods may have severe and possibly life-threatening
reactions if they eat them. The most common food allergy triggers are the proteins in cow's milk,
eggs, peanuts, wheat, soy, fish, shellfish and tree nuts. Food allergy occurs more frequently in
children than adults. Many of these children may lose their sensitivity to particular foods over
time.
Foods and other allergens, including penicillin, insect stings and latex, can trigger a severe,
systemic allergic reaction called anaphylaxis. Anaphylaxis is caused by swelling throughout the
body, and can involve several organ systems. Symptoms of anaphylaxis include a feeling of
warmth, flushing, tingling in the mouth or a red, itchy rash. Other symptoms may include feelings
of light-headedness, shortness of breath, severe sneezing, anxiety, stomach or uterine cramps,
and/or vomiting and diarrhea. In severe cases, patients may experience a drop in blood pressure
that results in a loss of consciousness and shock. Without immediate treatment with an injection
of epinephrine (adrenalin), anaphylaxis may be fatal.
Sinusitis and otitis media are other common allergic diseases that often are triggered by allergic
rhinitis. Sinusitis is an acute or chronic inflammation of the nasal sinuses, which are hollow
cavities within the cheek bones found around the eyes and behind the nose. This condition
affects over 15% of the U.S. population. Otitis media—or ear infections—is the most common
childhood disease requiring physician care. If not properly treated, it can affect a child's speech
and language development.
You can learn more about various allergic diseases by reading the appropriate Tips brochures in
this series.
Diagnosing and treating allergic reactions
An allergist is best qualified to treat allergic diseases. To determine if you have an allergy, your
allergist will take a thorough medical history and perform an exam. If indicated, he or she will then
perform allergy skin testing, or sometimes blood testing, to determine precisely which substance
is causing your allergy. Once your allergy triggers are identified, your physician can help you
establish a treatment program. The first step is to minimize your exposure to your particular
allergens to whatever extent possible. Your physician may also prescribe medications to reduce
allergic symptoms as well as inflammation.
Immunotherapy, also known as allergy shots, may also be recommended to modify your immune
response. For many patients, immunotherapy can help diminish their reactions to allergens.
Please see the Tip brochure in this series for more information on allergy shots.
In summary, an allergic reaction is a complex chain of events that involves many cells, chemicals
and tissues throughout the body. While there is not yet a cure for allergic disease, there are many
treatments available to lessen symptoms. See your allergist to determine the best course of
treatment.