Allergy
An allergy is an
immune system response to something
which is not directly dangerous to the body. The word derives from the
Greek words allos meaning
"other" and ergon meaning "reaction" or "reactivity".
History
The term and concept of "allergy" were coined by
Viennese
pediatrician Baron
Clemens von Pirquet in
1906. He observed that the
symptoms of some of his patients might
have been a response to outside
allergens such as
dust,
pollen, or certain foods.
Signs and symptoms
Allergy is characterised by a local or systemic
inflammatory response to
allergens. Local symptoms are:
Systemic allergic response is also called
anaphylaxis. Depending of the rate of
severity, it can cause cutaneous reactions,
bronchoconstriction,
oedema,
hypotension,
coma and
death.
Hay fever is one example of an
exceedingly common minor allergy - large percentages of the population
suffer from hayfever symptoms in response to airborne pollen.
Asthmatics are often allergic to
dust mites. Apart from ambient
allergens, allergic reactions can be due
to
medications.
Diagnosis
Generally, diagnosis of allergy is based on the medical history and a
brief
physical examination. When there is
diagnostic uncertainty, or when
hyposensibilization is considered,
testing for specific antigens can be useful.
Laboratory tests:
full blood count (occasionally there is
an increased
eosinophil count),
erythrocyte sedimentation rate or
C-reactive protein,
renal function and
electrolytes. Total IgE (an
immunoglobulin important in allergy) and
a RAST (radioallergosorbent test) can identify allergies.
Specific tests:
- Type 1 allergies (the commonest, see below) are often diagnosed
with skin-prick testing. This involves making a small scratch on the
skin and applying a number of suspected allergens. A true-positive (histamine)
and a true-negative (saline)
are usually applied as controls.
- Type 4 allergies (contact
eczema) need patch testing, which involves applying the
allergen on a patch of skin under a large plastic plaster.
Treatment
The only known mainstream medicine treatment for allergy is
hyposensibilization. Other treatments
are symptomatic: these include
antihistamines and
cortisone, can have the effect of
reducing the
symptoms.
In the
1960s, Dr. Len McEwen in the
United Kingdom developed a treatment for
allergies known as
enzyme potentiated desensitization, or
EPD. EPD uses much lower doses of antigens than conventional treatment, with
the addition of an enzyme. EPD is available in the United Kingdom and
Canada, and was available in the
United States until
2001, when the
Food and Drug Administration revoked its
approval for an investigative study being performed. Since that time an
American counterpart to EPD, known as
Low Dose Antigens, or LDA, has been
formulated from components approved by the FDA, and is available for
treatment from a small number of doctors in the United States. EPD (and LDA)
is still considered experimental by many mainstream doctors and medical
insurance companies, and many doubt that it is more effective than a
placebo.
In
alternative medicine, a number of
treatment modalities are considered effective by its practitioners in the
treatment of allergies, particularly
traditional Chinese medicine. However,
none of these have been backed up by good quality evidence. On the contrary,
they are generally criticised by mainstream medical researchers to be mainly
supported by anecdotes, which make them suspectible to be placebos.
Pathophysiology
Immunopathology
Recent research has shed some light on the mechanism by which many
allergies operate, but this is by no means the whole story; some causative
factors and allergenic pathways have yet to be explained.
There are four types of immune reactions (Gell &
Coombs-classification):
- Type 1: IgE-mediated (anaphylactoid)
- Type 2: IgG-mediated
- Type 3: Arthus reaction (serum sickness)
- Type 4: Cellular immunity (T
cell-mediated)
Certain individuals appear predisposed to the development of
allergies. The combination of
allergic rhinitis and
conjunctivitis,
atopic eczema and
asthma is termed the "atopic
syndrome".
It is presumed that predisposed individuals develop Type 1 allergy
against a number of very abundant allergens, such as the
house dust mite excrement and
grass pollen. All allergens are
protein-based.
Allergy is
immunologically a very complicated
mechanism, but the main mechanism is the production of
IgE antibodies against specific
allergens. The antibodies are coated to
mast cells, a type of
cell present in
epithelial tissues. When the allergen
comes into contact with IgE, the mast cell degranulates and
releases
histamine and a number of other
compounds that stimulate a local
inflammatory reaction. As the skin and
the nasal and conjunctival epithelia are most prone to come into contact
with allergens, this is also the place where allergic symptoms develop most
commonly.
Food allergy is a similar process
directed against food-borne allergens, leading to
diarrhea and
abdominal pain. The anaphylactoid
reaction is very quick (seconds to minutes); any set of complaints lasting
longer is probably due to another cause.
The hygiene hypothesis
One theory that has been gaining strength is the "hygiene hypothesis".
This theory maintains that since children in more affluent countries are
leading a cleaner and cleaner life (less exposure to dirt, extra use of
disinfectants, etc), their immune systems have less exposure to
parasites and other pathogens than
children in other countries or in decades past. Their immune systems may
have therefore many "loaded guns", cells which might have targeted, say, the
intestinal worms that no longer cause trouble in affluent neighbourhoods.
Having no reasonable target, these cells inadvertently become activated by
environmental
antigens that might only cause minor
reactions in others. It is the symptoms of this exaggerated response that is
seen as the allergic reaction.
Many common allergies such as asthma have seen huge increases in the
years since the second world war, and many studies appear to show a
correlation between this increasingly affluent and clean lifestyles in the
west. This is supported by studies in less developed countries that do not
enjoy western levels of cleanliness, and similarly do not show western
levels of incidences of asthma and other allergies. During this same period,
air quality, at one time considered the "obvious" cause of asthma, has shown
a considerable improvement. This has lead some researchers to conclude that
it is our "too clean" upbringing that is to blame for the lack of immune
system stimulation in early childhood.
Alternative views
Another theory is the exponential use and abuse of chemicals in
affluent nations since the second world war. Vast numbers of chemicals are
introduced into our indoor and outdoor environments with little or no
testing regarding their toxicity to living beings. Many believe that air
quality is getting worse rather than better, particularly if one considers
indoor air quality as well as outdoor. (Indoor air quality has become
significantly worse since building codes changed in the
1970s to make buildings more air-tight
and therefore to conserve energy. This affects buildings built since this
time.) Adverse reactions to toxins vary considerably from one person to
another, and can involve extremes in symptoms including the
neurological and
endocrine systems as well as the more
commonly recognized allergy symptoms listed above.
Allergies are also viewed by some medical practitioners as a negative
consequence of the use and abuse of
antibiotics and
vaccinations. This mainstream Western
approach to treatment and prevention of infectious disease has been used in
the more affluent "First
world" for a longer period ot time than in the rest of the
world, hence the much greater commonality of allergies in the First world.
It is hypothesized that use of antibiotics and vaccination affect the
immune system, and that allergies are a
dysfunctional immune response. There is however very little evidence to
support this view.
Allergies
:Which one of the following are you allergic
to?
(Many allergy sufferers are allergic to more than one, and sometimes all of
the following. Fortunately, most of the products we offer have multiple uses
and benefits. If you are not sure about what you are allergic to, we suggest
you see a physician.) Dust Mites, Pet Dander, Mold, Pollen ,Adult Asthma ,
Childhood Asthma, Latex, Formaldehyde ,Sinus Pain
