Allergy Overview
What are allergies?
Allergies are the immune system’s inappropriate and exaggerated response to a
foreign substance. Exposure to what is normally a harmless substance, such as
pollen, causes the immune system to react as if the substance is harmful.
Substances that cause allergies are called allergens.
When you come into contact with an allergen, you may experience
a number of symptoms including itchy, watery nose and eyes; asthma symptoms such
as wheezing and coughing; or hives.
What is an allergic reaction?
An "allergic reaction" is the result of how three factors interact in the
body:
1. The allergen — Allergens include pollen, mold, animal dander,
dust mites, medications, foods, latex, and others.
2. Mast cells — Although mast cells are found throughout the
body, most reside in connective tissues such as those of the skin, tongue, the
lining of the nose and intestinal tract, the lungs, and upper airways. Similar
cells, called "basophils" are present in the circulation.
3. Immunoglobulin E (IgE) — IgE is an allergic antibody, a type
of protein made by the immune system to recognize and fight specific body
"invaders." IgE coats the surface of the mast cells in tissues and basophils in
the bloodstream.
The first time an allergy-prone person is exposed to an allergen
(such as pollen), large amounts of the corresponding IgE antibodies (for
example, pollen IgE antibodies) are produced. The IgE antibodies cause the mast
cells to release inflammatory chemicals that cause swelling of tissues, as well
as histamine and several other chemicals that cause itching, engorgement of
blood vessels, increased secretions, and bronchospasm (tightening of muscles
that surround the airways). Some of these chemicals attract white blood cells
known as eosinophils. The eosinophils add more inflammatory chemicals.
If the allergen is in the air, the allergen is inspired
(breathed in), and an allergic reaction will occur in the eyes, nose, and/or
lungs. If the allergen is ingested, an allergic reaction will occur in the
mouth, stomach, and intestines. Sometimes enough inflammatory chemicals are
released to cause a reaction throughout the body, such as hives, decreased blood
pressure, shock, or loss of consciousness. This severe type of reaction is
called anaphylaxis and may be life-threatening.
What are the symptoms of allergies?
Allergy symptoms can be categorized as mild, moderate, or severe (anaphylactic).
- Mild reactions include local symptoms (affecting a specific area of
the body) such as a rash or hives; itchy, watery eyes; and some congestion.
Mild reactions do not spread to other parts of the body.
- Moderate reactions include symptoms that spread to other parts of
the body. Symptoms may include itchiness, hives, and/or swelling, that
spreads or difficulty breathing.
- A severe allergic reaction, known as anaphylaxis, is a rare,
life-threatening emergency in which the body’s response to the allergen is
sudden and affects the whole body (systemic). Anaphylaxis may begin with
severe itching of the eyes or face and. within minutes, progress to more
serious symptoms, including throat swelling (which could result in
difficulty swallowing and breathing); abdominal pain; cramps; vomiting;
diarrhea; hives (urticaria); and swelling (angioedema). Mental confusion or
dizziness may also result, since anaphylaxis may cause a drop in blood
pressure.
Types of allergies
People can be allergic to a wide variety of substances, the most common of
which are pollen and dust mites. Airborne allergens include:
- Pollen
Seasonal allergic rhinitis, or hay fever, is the allergic response to
pollen. It causes inflammation and swelling of the lining of the nose and of
the protective tissue of the eyes (conjunctiva).
Symptoms include sneezing, congestion, and itchy, watery eyes.
Treatment options include over-the-counter and prescription antihistamines,
anti-leukotrienes, nasal steroids, and nasal cromolyn. Some individuals may have
allergic asthma symptoms (wheezing, shortness of breath, chest tightness)
provoked by pollen exposures. Avoidance measures can be very effective for
helping reduce symptoms; these include avoiding pollen exposure by staying
indoors when pollen counts are high, closing windows, and using air
conditioning. Immunotherapy, or allergy shots, also may be used to treat pollen
allergy.
- Dust mites
Dust mites are microscopic organisms that live in dust and in the fibers
of household objects, such as pillows, mattresses, carpet, and upholstery.
Dust mites especially love warm, humid areas.
The symptoms of dust mite allergy are similar to those of pollen
allergy. To help manage dust mite allergies, try using dust mite encasements
(airtight plastic/polyurethane covers) over pillows, mattresses, and box
springs. Also, remove carpet, or vacuum frequently while using a vacuum cleaner
with high-efficiency filters. Treatment may include medications to control
nasal/eye and chest symptoms. Immunotherapy may be recommended for people whose
symptoms are not adequately controlled with avoidance and medications.
- Molds
Molds are parasitic, microscopic fungi (like Penicillium) with
spores that float in the air like pollen. Mold is a common trigger for
allergies and can be found indoors in damp areas, such as the basement or
bathroom, as well as in the outdoor environment in grass, leaf piles, hay,
mulch, or under mushrooms. Mold spores peak during hot, humid weather.
Treatment may include medications to control nasal/eye and chest
symptoms. Immunotherapy may be recommended for people whose symptoms are not
adequately controlled with avoidance and medications.
- Animal dander
The proteins secreted by sweat glands in an animal’s skin, which are
shed in dander, and to a lesser extent the proteins present in an animal’s
saliva, can cause allergic reactions in some people. No avoidance measures
can compare with elimination of the pet from the home. However, as many
people are reluctant to do this, second-best measures include restricting
the pet from the bedroom, using air cleaners with HEPA filtration, and
washing the pet (cat or dog) frequently.
Treatment may include medications to control nasal/eye and chest
symptoms. Immunotherapy may be recommended for people whose symptoms are not
adequately controlled with avoidance and medications.
Other allergens include:
- Latex
A latex allergy may develop in some individuals after some sensitizing
contact with latex due to occupational exposures or frequent surgical
procedures. Rubber gloves are a major source of allergic sensitization and
reactions. Skin rash, hives, eye tearing and irritation, wheezing, and
itching of the skin may occur in persons with latex allergy. Allergic
reactions to latex can range from skin redness and itching to more severe
reactions if there is exposure of the mucosal membranes, such as would
happen during an operation or during a dental or gynecologic exam.
Treatment of latex reactions begins by removing the offending
latex product. If you have latex allergy, it is important for you to wear a
Medic Alert bracelet and carry an emergency epinephrine kit. All procedures
should be carried out in a "latex safe" fashion. There is no cure for latex
allergy, so the best treatment for this condition is prevention.
- Certain foods
Food allergies develop when there is an IgE antibody to a specific food.
An allergic reaction occurs within minutes of eating the food, and symptoms
can be severe. Shellfish, peanuts, and tree nuts are the most common food
allergies in adults. Milk, egg, soy, wheat, shellfish, peanuts, and tree
nuts are the most common food allergies in children. Non-allergic food
intolerance is more common than true food allergy.
Symptoms of food allergy include itching, hives, nausea,
vomiting, diarrhea, difficulty breathing, and swelling in the area around the
mouth.
The only treatment is to avoid the foods that cause allergy
symptoms. If you (or your child) have food allergy, your doctor may prescribe
injectable epinephrine (adrenaline) for you to carry at all times, This is
necessary in case, despite diligent avoidance, you (or your child) inadvertently
consume(s) the food you (or your child) are (is) allergic to.
- Insect venom (stings)
If stung by a bee, the bee usually injects a sac of venom and may leave
a stinger in the victim's skin. If the stinger is still in the skin, gently
scrape it out with a fingernail or a stiff-edged object like a credit card.
Do not pull on the stinger, as this will cause the release of more venom
into the skin.
A normal reaction will result in pain, swelling, and redness
around the sting site. A large, local reaction may occur that will result in
swelling that extends beyond the sting site. For example, a person stung on the
ankle may have swelling of the leg. The most serious reaction to an insect sting
is an allergic one, requiring immediate medical attention. Symptoms of an
allergic reaction to an insect sting include difficulty breathing; generalized
hives that appear as a red, itchy rash that spreads to areas other than the
immediate area stung; swelling of the face, throat, or mouth tissue; wheezing or
difficulty swallowing; restlessness and anxiety; rapid pulse; and dizziness or a
sharp drop in blood pressure. If such a reaction has occurred, a re-sting has
the potential to cause a serious reaction that can be life-threatening.
An allergic reaction is treated with epinephrine (adrenaline),
either self-injected or administered by a doctor. Those who have had allergic
reactions from bee stings should be seen by a board-certified allergy/immunology
physician to confirm allergic potential by skin and/or blood testing to bee
venom. Administration of venom immunotherapy is recommended when venom allergy
is confirmed, to reduce the possibility that re-sting will cause a serious
reaction.
What is allergic rhinitis?
Nasal allergy symptoms and hay fever are referred to as "allergic rhinitis."
Seasonal allergic rhinitis describes nasal allergies that change with the
seasons due to pollen from plants (trees, grasses, or weeds). Seasonal symptoms
arise during the pollinating seasons for particular plants. Because you can be
allergic to more than one thing, your symptoms may get worse at different times
throughout the year, or they may appear constant (perennial).
Does everyone get allergies?
No. Most allergies are inherited, which means they are passed on to children
by their parents. People inherit a tendency to be allergic, although not to any
specific allergen. If a child develops an allergy, it is very likely that at
least one of his or her parents has allergies.
How common are allergies?
An estimated 50 million Americans, or 1 in 6 people, now have allergic
rhinitis. Allergic disorders are the sixth leading cause of chronic illness in
the United States, according to the Allergy Report from the American Academy of
Allergy, Asthma and Immunology.
How are allergies diagnosed?
If you think you have allergies, don’t wait to see if your symptoms will go
away. When your symptoms last longer than a week or two and tend to recur, make
an appointment with an allergy/immunology specialist so a complete evaluation
can be performed.
Allergy skin testing may be used to identify the allergens that
are causing your allergy symptoms. The test is performed by pricking your skin
with an extract of an allergen, and then evaluating the skin’s reaction.
If a skin test cannot be performed, a radioallergosorbent blood
test (RAST) may be taken, although its results are not as sensitive as a skin
test. This RAST evaluates the number of antibodies produced by the immune
system. Elevated levels of certain antibodies can identify particular allergies.
How are allergies treated?
The most important aspect of treatment is avoidance, but these measures will
usually be incomplete. Medications such as antihistamines, decongestants, or
a combination of both are available over-the-counter or by prescription to treat
allergy symptoms. Nasal sprays such as topical nasal steroids and cromolyn
sodium also can be used to treat allergy symptoms. Asthma medications to reduce
symptoms due to allergy include inhaled steroids, inhaled and oral
bronchodilators, oral anti-leukotrienes, and injected medications including
omalizumab – a monoclonal anti-IgE antibody. Immunotherapy, or "allergy shot
therapy", is recommended for symptoms not adequately controlled with a
combination of avoidance measures and regular medication use, and has been shown
to be effective in properly selected patients with allergic rhinitis and/or
allergic asthma.
Can allergies be cured?
Allergies cannot be cured, but symptoms can be controlled using a
combination of avoidance measures and medications, and allergen immunotherapy in
properly selected cases.
©Copyright 1995-2009 The Cleveland Clinic Foundation. All rights reserved
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