Allergies are the immune system's
incorrect 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
Are Allergies?/ โรคภูมิแพ้
When you come into contact with
an allergen, you may experience a number of allergic symptoms, including
itchy, watery nose and eyes, asthma,
wheezing and coughing or hives.
Is An Allergic Response?
An allergic reaction is the
result of how three factors interact with the body:
- The allergen. Allergens
include pollen, mold, dust
- Mast cells. Though mast cells,
a type of white cell, 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.
- Immunoglobulin E (IgE). This
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.
The first time an allergy-prone
person is exposed to an allergen (such as pollen), large amounts of the
corresponding IgE antibody (for example, pollen IgE antibodies) are
During the next exposure, these
antibodies activate, causing the mast cells to release inflammatory
chemicals that lead to swelling of tissues, itching, engorgement of
blood vessels, increased secretions and tightening of muscles that
surround the airways (bronchospasm). Some of these chemicals attract
other white blood cells known as eosinophils. The eosinophils add more
If the allergen is in the air,
the allergic reaction will occur in the eyes, nose, and lungs. If the
allergen is ingested, the 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.
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. These may include
itchiness or difficulty breathing.
A severe reaction (anaphylaxis)
is a rare, life-threatening emergency in which the body's response to
the allergen is sudden and affects the whole body (systemic). It may
begin with acute itching of the eyes or face and within minutes progress
to more serious symptoms, including varying degrees of swelling as in
hives or angioedema
(if the airways or throat are involved in the swelling, this could
result in difficulty swallowing and breathing), abdominal pain, cramps,
vomiting, and diarrhea.
Mental confusion or dizziness may
also be symptoms, since anaphylaxis causes a quick drop in blood
Are The Common Types Of Allergies?
People can be allergic to a
variety of substances, the most common of which are pollen and dust
Pollen: Allergic rhinitis,
or hay fever, is the allergic response to pollen. It causes inflammation
and swelling of the lining of the nose, as well as the lining of the
eyes and eyelids (conjunctiva).
- Symptoms include sneezing,
congestion and itchy, watery eyes.
- Treatments include
over-the-counter and prescription antihistamines, nasal steroids,
and nasal cromolyn. Prevent pollen exposure by staying indoors when
pollen counts are high, closing windows and using air conditioning.
Dust mites: These are
microscopic organisms that live in dust. House dust is a mixture of
potentially allergenic materials including fibers from different
fabrics, dander from animals, bacteria, mold or fungus spores, food
particles, bits of plants or other allergens.
- Symptoms are similar to those
for pollen allergy and can also produce symptoms of asthma such as
wheezing and coughing.
- Treatments include medications
such as antihistamines or decongestants. Immunotherapy
may be recommended for people whose symptoms are chronic.
Molds: These 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 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. In some people, symptoms of mold allergy may be brought on or
made worse by eating certain foods, such as cheese processed with fungi.
- Symptoms include sneezing,
congestion, itchy, watery eyes, runny nose and coughing.
- Treatment with antihistamines
or corticosteroids is usually helpful, but avoiding these substances
is important also.
Animal dander: Proteins
secreted by oil glands in an animal's skin, as well as the proteins
present in an animal's saliva, cause allergic reactions in some people.
Allergies to animals can take two or more years to develop and symptoms
may not subside until months after ending contact with the animal.
- Symptoms include sneezing,
congestion and itchy, watery eyes.
- Treatments include avoiding
exposure to the animals causing your allergies if possible.
Medications such as antihistamines or decongestants may be helpful,
or immunotherapy may be recommended if your symptoms are chronic.
Other Allergies Are There?
Latex: Latex allergy
develops after some sensitizing contact with latex. Rubber gloves are
the main source of allergic reactions. A component of the latex
substance itself is an allergen for many people. The latex glove powder
is an airborne allergen, which causes upper airway allergic reactions in
some people, as well as worsening asthma.
- Symptoms include skin rash,
hives, eye tearing and irritation, wheezing and itching of the skin.
Allergic reactions to latex can range from skin redness and itching,
to much more serious symptoms such as difficulty breathing, hives,
or acute (sudden-onset) gastrointestinal problems.
- Treatments include removal of
the latex product and drugs according to the type of symptoms
developing. If you have latex allergy, it is important for you to
wear a MedicAlert bracelet and carry an emergency epinephrine kit at
all times. There is no cure for latex allergy, so the best treatment
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. Milk, fish and shellfish, nuts, peanuts, wheat and eggs are the
most common foods that cause allergies. Non-allergic food intolerance is
more common than true food allergy.
- Symptoms include asthma
(wheezing and coughing), hives, runny nose, vomiting, diarrhea,
swelling in the area around the mouth.
- The best treatment is to avoid
the foods that cause allergy symptoms. For rashes, skin creams may
ease discomfort, while antihistamines will help reduce itching,
congestion, and other symptoms. For more serious reactions,
corticosteroids such as prednisone will help to reduce swelling. In
life-threatening situations, an epinephrine (adrenaline) injection
immediately begins reversing symptoms and is the only effective
Insect venom (stings):
Everyone who gets stung by an insect will have pain, swelling, and
redness around the sting site. However, some people are allergic to
stings and have severe or even life-threatening reactions.
- Symptoms include difficulty
breathing; 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; dizziness or a sharp drop in
- You may take an oral
antihistamine, like Benadryl, to reduce itching, swelling, and
hives. To relieve pain, take aspirin or an aspirin substitute. An
allergic reaction is treated with epinephrine (adrenaline), either
self-injected or administered by a doctor. Usually this injection
will stop the development of severe allergic reaction.
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 plant pollens (from 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
Everyone Have 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.
Being exposed to allergens at
certain times when the body's defenses are low or weak, such as after a
viral infection or during pregnancy, may also contribute to the
development of allergies.
Common Are Allergies?
Allergic disorders affect more
than 20 percent of adults and children (40 to 50 million people) and are
the sixth leading cause of chronic illness in the United States,
according to the American Academy of Allergy, Asthma and Immunology.
Are Allergies Diagnosed?
If you think you have allergies,
don't wait to see if your symptoms go away. When your symptoms last
longer than a week or two and tend to recur, make an appointment with
your doctor so a complete medical
evaluation can be performed.
An allergy skin
test, also called a scratch test, may be used to identify the
substances that are causing your allergy symptoms. It is performed by
scratching an extract of an allergen placed on your skin 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 accurate as a skin test. This test
evaluates the number of antibodies produced by the immune system.
Elevated levels of certain antibodies can identify particular allergies.
Are Allergies Treated?
such as antihistamines, decongestants or a combination of both of these
medications can be taken over-the-counter or by prescription to treat
allergy symptoms. Nasal sprays such as topical nasal steroids and
cromolyn sodium can also be used to treat allergy symptoms. Immunotherapy,
or allergy shots, is recommended for relief needed over a long period of
Allergies Be Prevented?
Allergies cannot be prevented,
but they can be treated and controlled. Making changes in your environment
can greatly limit your exposure to certain allergens and reduce your
Not all allergies are created equal.
Food allergies can cause very different symptoms than pollen allergies.
But they all have one thing in common -- they're a defensive reaction by
your body's immune system to a substance that is usually harmless.
This section provides information
on the various types of allergies and allergy-related conditions. Each
article describes the recommended treatment for that condition. This
section also contains important information on how to handle
life-threatening allergic reactions, called anaphylactic reactions.
Here's a list of the complete
contents of this section:
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Medically Reviewed by Dominique S. Walton, MD, MBA, WebMD.