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Reviewed by Dr Victoria Lewis, specialist registrar in dermatology
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Definitions
Atopy is the general medical term for allergic conditions such
as hay fever, asthma or this type of eczema. People with a tendency to suffer
from allergic conditions are said to be atopic.
About 15 per cent of the population are affected by one or more
atopic conditions. Atopic eczema affects about 15 per cent of children and up
to 5 per cent of adults in the UK.
The
immune system of people with atopic
eczema is active in a particular way. They especially make large amounts of a
protein called IgE. IgE is one of a handful of proteins called immunoglobulins
or antibodies, the purpose of which are to act as catalysts for the protective
cells of the immune system to recognise and lock on to the protein components
of foreign invaders.
IgE is present in small amounts in everyone. However, in atopic
eczema more is produced because of increased sensitivity to substances which
are inhaled or eaten, or substances in contact with the skin. These could be
animal dander, foodstuffs, house dust mite, or bacteria or yeasts that live on
the skin in everyone and usually cause no problems. Most individuals with
atopic eczema react to all of these things to varying degrees.
The distinction between atopic eczema,
allergic contact eczema
('dermatitis') and
irritant contact eczema is that in
the first two the immune reaction sits in the middle and determines whether an
individual will or will not react. In irritant contact eczema the
antigen-antibody system is bypassed and the skin reaction occurs as a direct
result of the chemical effects of the irritant on the skin. In allergic contact
eczema the person slowly develops a skin reaction to a specific substance that
has been in contact with their skin.
Features of atopic eczema
Although the first episode of atopic eczema can be delayed to
adulthood the majority of people have a history that goes back to their
childhood. About half of affected children show improvement by the age of six
and 85 per cent by the time puberty starts.
About 70 per cent of people have a family history of at least
one of the atopic conditions. This points to genetic links to atopy but the
relationship is complex. A combination of genetics and environmental exposures
probably determine whether an individual develops atopic eczema, but we do not
yet know what the most important influences are.
The main symptom, as with all types of eczema, is itch.
Generally the skin is dry but the most affected skin looks red, with a slightly
raised but ill-defined margin when the eczema is active. Lumps or blisters,
some oozing of fluid from the skin surface and scaling of the skin are all
features of flare-ups.
After the acute episodes the skin will settle down to a less
active longer-term appearance, which is a bit less angry looking but shows more
in the way of thickening, scoring and darkening of the skin where it is most
scratched.
In infants and children the affected skin is mostly the face and
as they get a bit older the rash spreads to the body and limbs. The napkin area
is usually spared although it may be inflamed from the effect of urine or the
overgrowth of yeast organisms on the skin (thrush).
White children tend to get the most trouble on the ‘flexures’ –
the skin creases on the meeting surfaces of the joints. Elbows, wrists, behind
the knees and fronts of the ankles are typical.
Black and Asian children tend to be affected on the opposite
side of the joints, such as the point of the elbow or front of the knees.
Adults show more involvement of the face and trunk again.
Superficial infection of the skin causes increased redness and
heat, weeping and perhaps crusting. Small blisters may contain pus. Infected
eczema does not usually give signs of general infection such as a raised
temperature.
Tests
The diagnosis of atopic eczema is usually quite straightforward
on the basis of the symptoms, appearance and positive family history of atopy.
Although blood tests will be likely to show generally raised levels of the IgE
antibody this is not in itself either necessary or helpful to the
doctor.
The
IgE RAST test (a blood test) looks at
more specific allergens such as general food groups, house dust mite and animal
dander. However, these should be interpreted with caution and may only be
useful for a proportion of individuals with eczema. Your doctor may perform a
range of other
allergy tests if he or she believes
them to be beneficial.
Treatment
The following is an overview of treatments.
Avoid irritants
Easier said than done, especially when there may be many
possible allergens, when they are common items that are hard to avoid or when
it is unknown what the most important allergens are.
In general terms cotton clothing is less irritating, animal
dander such as from cats and dogs should be avoided as much as possible and
reasonable steps should be taken on the house to reduce general dust and house
dust mite levels.
Exclusions of foods are rarely helpful and are now little used
in treatment.
Moisturise the skin
Eczema is a dry skin condition and
moisturisers (emollients) are still a
mainstay of treatment. The problems of using enough moisturiser are mainly
practical ones. The skin still dries out during the course of the day, so
re-application is necessary but is often inconvenient to do.
Hand washing removes oils and moisture from the skin so there
should always be a supply of moisturiser at the sink (as well as a non-soap
based hand cleaner like aqueous cream or emulsifying ointment). Prescriptions
for moisturisers need to be of adequate amounts to enable their liberal
use.
Treat infection
It is perfectly normal for bacteria to be present on the
surface of our skin, but in eczema the skin defences are weakened, and
bacterial invasion of the deeper layers occurs, triggering immune reactions.
Flare-ups of eczema are very often due to infection and need treatment with
antibiotics.
Antibiotic creams are of limited value as they are poorly
absorbed but can be helpful in the short term for mild exacerbations, usually
in combination with a steroid cream. More active eczema needs antibiotics by
mouth over a course of a week to 10 days long.
Reduce inflammation
Until very recently steroid creams were the main
anti-inflammatory treatment but the newer ‘cytokine inhibitor’ creams look promising as
alternatives. Steroids are manufactured in different forms, with different
degrees of potency.
Although it is true that over-use of steroids can cause skin
problems such as thinning, it is important to keep this problem in perspective.
Cautious use of the minimum amount and potency is safe even in
the long term and the problems of under-treated eczema with all the knock-on
effects that arise from it are far worse than those from the use of steroid
creams to get it under control. This is especially true of children where a
reluctance to use steroid is understandable, but sometimes over
done.
Other treatments
These are used for eczema that is particularly hard to
control. Carefully controlled ultraviolet light treatment can be useful but
needs to be rationed to limit the increased risk of skin cancer in the long
term. Oral drugs that
dampen the immune system are the main
treatments for severe eczema and can be used in the medium to long term,
provided they are monitored for the occurrence of side effects. This usually
can be done by periodic blood tests. Short courses of steroids by mouth at
fairly high dose are sometimes also used to bring active eczema under control.
Evening primrose oil/gamolenic acid capsules have now been
discontinued as treatment for eczema as there has been no convincing evidence
that it works.
Chinese herbal treatment is also potentially problematic for
various reasons. Despite some apparent successes, the way in which it works is
unclear.
Some Chinese herbal products have been found to contain added
steroids and there is no regulation controlling either the safety of such
products or the qualifications of those prescribing them; therefore, at the
moment one can’t recommend them with any confidence.
Other types of eczema
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Based on a text by Helen Davis, pharmacist
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Last updated 15.09.2005
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