An allergy is a disorder of your immune defence
system that causes an abnormal response when
you come into contact with a particular substance.
Any substance that triggers this is called
an allergen. Contact may be with your skin,
or with the lining of your lungs, mouth, gullet,
stomach or intestine. Someone who suffers
a response to a particular allergen is said
to be allergic to it. There is a huge range
of allergens. Many are quite mild, but in
some cases the response is very severe, and
can even lead to death. Causes
Allergy runs in families.
The basic problem is a change (mutation)
in one or more genes passed on by the mother.
Someone with an allergic tendency produces
far more than the normal amounts of an antibody
called IgE (immunoglobulin class E) - an
antibody is a molecule of protein. Allergic
people also produce more than the normal
numbers of a particular kind of wandering
cell called a mast cell. IgE molecules can
get stuck onto the outside of mast cells
at special points called receptor sites.
When an allergen such as a pollen grain
comes along, it attaches itself to two or
more of the IgE molecules. The membrane
of the mast cell is then distorted and tears.
Unfortunately, mast
cells are full of some very irritating substances,
especially histamine (see media 'Allergic
rash on arm'). Histamine has many effects
when released.
- It makes smooth
muscles contract, including those in the
walls of the air tubes of your lungs.
- It increases the
leakage of fluid from small veins, so
that membranes swell.
- It stimulates mucus
and watery secretion from your nose lining
and causes local itching and burning.
There are thousands
of allergens, most of them familiar as everyday
items such as various food substances, food
additives, washing powders and so on. But
here are some that you may not know about:
- Food-related things:
green coffee beans; dust from tea and
various kinds of bean, including coffee;
spores from mouldy cheese; mushroom compost;
and weevil-infested wheat flour
- Dust, powders or
pulp from things such as wood, cork or
tobacco
- Irritant gases
and fumes, such as from soldering and
smoke
- Clothing-related
things: silk, cotton, dyes
- Resins and gums,
solvents and paint
- Chemicals such
as those used in hairdressing, or isocyanates,
formaldehyde or salts of chromium, nickel,
cobalt, platinum and vanadium
- Animal products,
especially urine
- Various drugs,
especially antibiotics, cimetidine and
piperazine, or drugs in powder form
- Plants
- Biological enzymes
- PVC
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Allergies
