An allergy is an abnormal sensitivity or reaction of your immune system to a substance (an allergen) that you eat, inhale or touch. Non-allergic people can usually tolerate this substance.
Nearly 50% of all people who suffer from allergies have hay fever.
If both parents have allergies, their children are more likely to develop an allergy, although not always the same kind of allergy.
Almost 70% of adults with food allergies are younger than 30 years and most children are under three years old.
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The function of the immune system is to protect the body against foreign substances
or hostile invaders such as viruses, bacteria and harmful chemicals. When such
a substance enters the body, the immune system reacts by producing proteins called
antibodies or by sending specific white blood cells called eosinophils to that
area.
Eosinophils attack infection, viruses, bacteria and other foreign substances.
It is also these white blood cells that cause the immune system to overreact
while they "attack" an invader, which usually is a substance harmless to other
people.
Antibodies against harmful substances are produced by beta-lymphocytes, the
body’s white blood cells that are responsible for fighting infections. Antibodies
attach themselves to the substances and set off a reaction that destroys them.
Antibodies usually leave harmless substances alone.
The immune system produces five kinds of antibodies, each with its own function.
Allergic reactions involve the IgE antibody. Allergic persons form IgE antibodies
against substances that are harmless in most individuals, such as certain types
of food and pollen, called antigens or allergens. Once the IgE antibodies are
formed against a specific allergen, they bind to special mast cells which are found in the skin, lungs, nose and intestines and are also known as basophils which circulate in the blood. This process
is called allergic sensitisation.
When a person is exposed to that specific allergen again, the IgE antigens
attached to mast cells and basophils bind to the allergen, causing a reaction
that causes the mast cell to burst. When the mast cell bursts (also called degranulation
of mast cells), it releases chemicals such as histamine. These chemicals make
the blood vessels dilate and smooth muscles contract. For example, the smooth muscles
of the bronchi contract and the air passage narrows, which may lead to asthma.
These chemicals also attract eosinophils to that area. The eosinophils release
chemicals that neutralise the chemicals released by the mast cells.
When the allergic reaction is severe, e.g. to a food allergen such as shellfish or a medicine such as penicillin or aspirin, so much histamine is released that the
person’s blood pressure drops, blood circulation slows down and the bronchi
contract, causing respiratory distress. Such a severe allergic reaction is called
anaphylactic shock and may cause death. Fortunately this is rare.
Cause and symptoms
The cause of most people’s allergies is not known. However, an allergy usually
begins with sensitisation when the person is exposed to an allergen. This period
may last from several days to a few decades. The repeated exposure to an allergen
triggers the immune system to form the antibodies that cause the allergic reaction
to the specific allergen.
Allergies are classified according to the substances causing them or the parts
of the body they affect.
Respiratory allergies
Allergic rhinitis (nasal allergy or allergies of the nose)
Breathing air that contains an allergen causes allergic rhinitis, the most common
respiratory allergy. It often begins around the age of two years, but the most
common age when this allergy to airborne allergens begins is the late teens
or early 20s. Allergic rhinitis is also sometimes called hay fever. Other respiratory
allergies include those that affect the sinuses (allergic sinusitis), bronchial
tubes (asthma) and lungs (hypersensitive pneumonitis).
Allergic rhinitis is usually seasonal. The most common allergens are grass or tree pollens spread by the wind. Hay fever is therefore a misleading
name, since it is not caused by hay (it also does not produce fever). Perennial
allergic rhinitis, which occurs all year round, is usually a reaction to indoor
allergens such as moulds, dust and dust mites, as well as animal dander. Dander
is the flakes of dried animal skin, saliva and urine that cause an allergic
reaction. Sometimes it is wrongly assumed that people who are allergic to pets
are allergic to their fur or hair.
Symptoms of allergic rhinitis, especially the seasonal form or hay fever are worse when the specific allergen, e.g. grass or tree pollen is present in the air
and may grow worse over a number of years. Sometimes symptoms lessen slightly
with age. The symptoms of allergic rhinitis include:
Continuous sneezing, especially after waking up in the morning
Runny nose and a postnasal drip
Stuffy nose, which may be accompanied by frequent sniffing
Watery eyes that are also itchy
Itchy ears, nose and throat
Continuous rubbing of nose (in children)
"Allergic shiners" – dark circles under the eyes
Discomfort in the facial area
Irritability
Tiredness or loss of energy
Rhinitis of pregnancy
Pregnant women sometimes have some of these symptoms without suffering from
allergic rhinitis. This is called rhinitis of pregnancy. The cause is unknown,
although hormones released during pregnancy may be the cause of swelling in
the mucous lining of the nose. The higher circulating blood volume during pregnancy
– 40% above the levels of non-pregnant women – may also congest the nasal passages.
Asthma
The main causes of asthma, an abnormal reaction in the lower airways, are environmental
exposure and allergies to allergens such as pollen, mould spores, animal dander
and dust mites. Other allergies, e.g. eczema and allergic rhinitis, are linked to asthma, especially in children.
Skin allergies
Contact dermatitis
This skin allergy, characterised by itchy rashes, often occurs in children.
It is caused by contact with a natural substance such as cat fur or a manufactured
item such as soap that becomes an allergen.
Atopic dermatitis or eczema
Although it has no known cause, heredity is thought to play a role. Children
who have a family history of allergies are prone to eczema, as are those who
are allergic to milk, eggs, peanuts, soy, wheat or fish. Children who suffer
from eczema are also more likely to develop other allergies later in life, such
as allergic rhinitis or asthma. This syndrome is called atopy.
Eczema is characterised by an itchy red rash that usually starts on the cheeks
and usually involves the folds of the elbows, the back of the knees and behind
the ears. In its severe form it is characterised by an itchy red and raw rash that involves the entire body. Scratching quickly spreads the rash and may lead to oozing
and the forming of a crust.
Hives or urticaria
Lasting for minutes or days, hives (also called weals or welts) are large, itchy
red bumps on the skin. Hives can also last for longer months to years and are then
referred to as chronic urticaria. These hives can be one or many bumps, and
vary greatly in size and shape. Although they more commonly appear on the arms,
legs and trunk, they can appear anywhere on the body as a result of the body’s
reaction to factors such as certain foods, pollen, animal dander, drugs, insect
bites, cold, heat, light or emotional stress. The release of histamine from mast cells in the skin causes the hives to form.
Hives are generally not an emergency, but when they appear suddenly, spread
rapidly and are accompanied by a swollen throat, tightness of the chest, wheezing
or difficulty breathing, this indicates a severe allergic reaction that requires
immediate medical attention.
Food allergies
More than 70% of people who have a food allergy are younger than 30 years.
Adults account for only about one to two percent of people who are allergic
to food or some substance in food. Although one in 12 children are suspected
to have a food allergy, only one in 25 children are usually confirmed as having
a food allergy.
Any food may cause an allergic reaction, but the prime causes are proteins
in cow’s milk, egg white, peanuts, wheat and soybeans. Other less common causes
include berries, shellfish, maize, beans, gum arabic, and the food colourant
tartrazine, which is added to some green, orange and yellow foodstuffs. An allergic
reaction to food usually occurs within half an hour of eating it, but can also
occur within only five or 10 minutes or after four to six hours.
It is sometimes difficult to establish which allergens are responsible for
a food allergy, because reactions to certain foods are sometimes delayed or
they may be caused by food additives or eating habits. A food allergy causes
a variety of symptoms in the skin, digestive tract and respiratory system. Anaphylactic
shock can result in severe cases. Symptoms of a food allergy are:
Dizziness
Perspiring
Faintness
Vomiting
Stomach cramps
Nausea
Diarrhoea
Swelling of the face and tongue, and respiratory congestion (severe cases)
Drug allergies
The most common allergy in this category is a reaction to drugs in the penicillin
family. Other drugs that can trigger allergic reactions include:
Sulphas
Barbiturates
Anticonvulsants
Insulin
Local anaesthetics
Dyes injected into blood for X-ray purposes
Aspirin
Insect sting allergies
It is thought that people who have allergies such as food, drug or respiratory
allergies are more prone to insect sting allergies. The venom in the stings
of bees, wasps, hornets, yellow jackets and fire ants is the common allergen
triggering this type of allergic reaction.
If people know they have an allergy to insect stings and that they can easily
come into contact with the venom, it is best for them to carry a single-dose
injection kit of adrenaline. Injecting themselves with the adrenaline will help
counteract and alleviate allergic symptoms until they can receive medical attention.
Prevalence
Allergies occur across the age, sex and race spectrum. An allergy can start at
any age. Children are most vulnerable to allergies, especially allergic rhinitis.
Boys younger than 10 years are twice as likely as girls in this age group to have
symptoms of allergies to airborne substances.
Course
Of the five different classes of antibodies that the immune system produces, those
belonging to the IgE class are formed in reaction to allergens. These antibodies
bind with the allergen and attach to two types of defensive cells, namely the
mast cells and basophils. The cells in turn produce mediators (the best known
being histamine), which are responsible for the symptoms of an allergic reaction
such as sneezing, runny nose and itching.
As soon as the cells have produced these mediators, "reinforcements" in the
form of eosinophils, a type of white blood cell, are attracted to the area where
the reaction is taking place, producing an even more intense reaction.
If left untreated, allergic rhinitis in children may lead to complications
such as regular ear infections, which may in turn influence speech development
in young children. It is important to note that there is no indication that
children actually outgrow the tendency to be allergic. They may outgrow a specific
allergy but develop another one. Allergic reactions tend to subside with age,
but adults seldom "outgrow" allergies.
Risk factors
Heredity
Environment
Upper respiratory infections
Heredity – if one parent is allergic, a child runs a risk of 30 to
50% of inheriting the tendency to be allergic, although he or she may not
necessarily develop the parent’s particular type of allergy. If both parents
have allergies, their children have a 60 to 80% likelihood of developing allergies.
Only 25 to 50% of identical twins share the same type of allergy.
Environment – although heredity determines whether you will have
an allergy of some sort, it is usually the environment that sets the process
in motion. The environmental factor has an influence when you are in a place
where you are exposed to high levels of a specific antigen, especially early
in life.
Upper respiratory infections – children who contract viral or bacterial
infections of the upper respiratory system (nose, throat and bronchial tubes)
before they are six months old are more likely to develop allergies or conditions
such as asthma later on in life.
Although emotional stress may trigger an allergy, allergies do not have a psychosomatic
origin.
When to see a doctor
Always consult a health professional when you have the following symptoms:
Violent stomach cramps, vomiting, bloating or diarrhoea – you could have
food poisoning, a serious allergic reaction to food or another kind of allergic
reaction.
Painful or difficult breathing – get medical treatment immediately. You
could be having an asthma attack, another serious allergic reaction or a heart
attack.
Sudden development of hives, accompanied by severe flushing and itching,
and rapid heartbeat – you need urgent medical attention, as these symptoms
could indicate the onset of anaphylactic shock
Pain in the sinus area, fever and a yellow or green discharge from the nose
– you may have a sinus infection
A cough or cold that does not subside within a week or two
Swelling of the face around the eyes and lips
Also consult your doctor if non-prescription allergy medicines do not relieve
your allergy symptoms, or if the symptoms suddenly get worse for no apparent
reason.
Diagnosis
As a number of conditions resemble allergies but do not involve the immune system,
it is not always easy to diagnose an allergy. In the case of a mild allergy, tests
may not be necessary and your general practitioner or family doctor can base his
or her diagnosis on your medical history and a thorough physical examination.
However, certain laboratory tests are suggested when the allergy is severe.
A clinical immunologist usually performs these tests.The following laboratory
tests may be done to verify the cause of an allergy:
Complete blood cell count – although not always routinely used for
allergy testing, this blood test is performed to detect an increase in the
eosinophil white blood cell count. If the test results show a higher than
normal number of these white blood cells, it is an indication that the body
is trying to fight off a foreign invader such as an allergen. (A high count
of eosinophil white blood cells is also found in people with Churg-Strauss
syndrome.)
Nasal smear – a sample of mucus obtained from the nose is examined
for an increase in eosinophil white blood cells.
Radio-allergosorbent (Rast) test – the amount of IgE antibodies in
the bloodstream is measured in serum that recognises allergens inhaled by
the patient. It is therefore also a reliable test for inhalant and food allergens.
If the test results show a high amount of IgE antibodies against a certain
allergen, it is highly probable that the person has an allergy to that allergen.
Skin test – if it is not clear from someone’s medical history what
he/she is allergic to, a skin prick test may be done. In this test, a solution
of a suspected allergen is injected into the skin to determine whether there
is IgE immunologic hypersensitivity. If the person is allergic, a small hive
and redness around the hive (flare) will appear within 15 to 20 minutes on
the skin area where the test was done. This test yields the best results when
testing for inhalant allergies, insect sting allergies and drug allergies.
It can also help to determine whether you have food allergies.
These tests are not completely reliable; if too much of the substance is injected,
it may cause a reaction in a non-allergic person. In addition, extremely sensitive
people may go into anaphylactic shock when even just a tiny amount of the substance
is injected into their skin.
If the doctor’s prescribed treatment does not alleviate your symptoms or the
doctor suspects you may have another problem, more advanced tests may be necessary.
These include X-rays or a CAT scan of the sinuses
to detect sinusitis or structural nose defects. A nasal
endoscopy, which enables the surgeon to look inside the nose passages with a
lighted, flexible tube, may be done to look for structural defects, infections
or nasal polyps.
Treatment
Medication
There is no cure for allergies. The best way to control or treat any allergy
is to avoid the triggering substance. However, this may be difficult. The most
common treatments are:
Antihistamine – blocking the release of histamine by the body’s mast
cells in body tissue (histamine causes the allergic reaction).
Decongestants – shrinking swollen nasal tissues, thereby relieving
congestion. These drugs are sometimes combined with an antihistamine and control
nasal symptoms effectively.
Steroids – controlling inflammation and stopping allergic reactions.
At the same time, these anti-inflammatory substances reduce nasal swelling
and mucous secretions.
Topical creams or skin ointments – for eczema
Immunotherapy or allergy injections – can gradually build tolerance
to the allergenic substance so that the body no longer reacts to it.
Antibiotics – may also be necessary to treat complications such as
the ear and sinus infections that are common in children with allergies.
There is a wide range of medicines for treating asthma. Usually more than one
type of medication is prescribed, firstly to relieve the symptoms during an
acute attack and secondly to control the symptoms over time.
Home
If you have had a severe allergic reaction in the past, you should always
carry a kit to treat anaphylactic shock and give yourself an injection from
the kit when necessary. It is important to get medical treatment immediately,
but while waiting for medical help to arrive, lie down with your legs raised
above chest level to increase the blood flow to your heart and brain.
Surgery
People with asthma are likely to suffer from complications during and after
surgery. Make sure your doctor knows that you have asthma, as you will probably
need to have a number of tests done before undergoing surgery.
You should also inform your doctor if you suffer from allergic rhinitis and
it is not possible to schedule the operation outside the "hay fever" season.
Other
No nutritional or herbal treatments or vitamin or mineral supplements have
been proven to be successful in treating allergies. If you are allergic to pollen,
you should be especially careful of herbal remedies, as they may contain the
very substances that activate your allergic symptoms!
Unless you are allergic to some food substance, you do not have to change your
diet to prevent an allergic reaction. As an allergy is not caused by a nutritional
deficiency but is a reaction of the immune system, taking vitamin and mineral
supplements will not help to prevent an allergic reaction.
Prevention
Depending on your specific allergies, some preventive maintenance at home could
help control the environment, thereby reducing the risk of allergic reactions.
These steps include:
Using special mattress and pillow covers to control dust mites
Frequent vacuuming and dusting to get rid of dust mites and other airborne
allergens
Using an air conditioner in your home and car and changing the filters often
Getting rid of old bedding, toys, clothing and other items that may be carriers
of dust and mould
Keeping pets outdoors as much as possible and off the furniture
Bathing pets regularly to reduce dander
Mopping uncarpeted surfaces regularly
Removing overstuffed furniture and carpets to reduce dust mites
Reviewed by Prof Eugene Weinberg, Allergy Diagnostic Unit, UCT Lung Institute.
Children are at risk of severe allergic reactions when they eat kiwi fruit, according to UK research. The two-year survey at Southampton General Hospital showed that children under five were particularly at risk.
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