There are 3 major skin diseases caused by allergies:
2. Allergic Contact Dermatitis
3. Hives (Acute Urticaria)
It is important to remember that any combination of the 3 can occur in the same
patient at the same or different times.
Eczema is a common allergic skin disease in infants. It usually develops around
4 months of age. In some cases the term eczema is used interchangeably with dermatitis.
Some prefer to reserve the term dermatitis, for cases of eczema caused by an external
trigger, as in the case of allergic contact dermatitis.
In most cases, eczema resolves itself in infancy or at least by the time the child
is 5 years old. It is usually the first symptom of the allergic march, often to
be followed by asthma or hay fever, as seen in atopics.
The symptom that occurs almost invariably in eczema is itching (pruritus). If this
symptom is not present, the diagnosis of eczema should be seriously questioned.
There are two forms of eczema. Acute eczema causes red, swollen patches on the skin,
with watery discharge (oozing), and usually causes severe discomfort. Chronic eczema
causes thickened, scaly skin patches, which often gets secondarily infected leading
to crusting. As the term implies, chronic eczema tends to last, sometimes for years
and in rare cases for life.
In infants, eczema usually appears on the cheeks, scalp, neck and trunk. In children
over two years old, eczema usually appears in the knee and elbow creases, the neck,
wrists and ankles. However, there is overlap between the age groups, and other areas
of the body may be involved.
Factors affecting Eczema
The exact cause of eczema is unknown, but we do know some of the factors that precipitate
or aggravate it. The main factor is heredity. About one-third of children with eczema
have parents or close relatives who have eczema, asthma or hay fever (are atopic).
Several studies have shown that, foods like milk, eggs, wheat, peanuts and soy are
common causes of eczema in infancy. It is advisable to skin test all infants with
severe eczema to these foods.
Skin irritants, such as soaps, detergents and wool can all aggravate eczema.
Climate can also trigger eczema. Babies who are brought from warm countries to areas
where the climate is cold are particularly vulnerable. Cold, dry air causes the
skin to become dry and itchy. A hot, humid climate can also cause sweating, which
worsens the itching and scratching in eczema.
2. Allergic Contact Dermatitis
This form of allergic skin disease occurs when a substance that comes in direct
contact with the skin causes an eczematous reaction. It is usually impossible to
tell the difference between atopic eczema and allergic contact dermatitis purely
by examination of the rash. A thorough history and a suspicious, detective's mind
is the most useful tool in helping to differentiate the two.
Poison Ivy is one of the most common and familiar causes of contact dermatitis.
Other leaves such as oak and sumac can also cause contact dermatitis. The resin
in the leaves is the offending agent.
Since new potentially sensitising chemicals are continually coming into use, the
prevalence of allergic contact dermatitis will only continue to increase.
Contact dermatitis is the most common occupational disease, and as such, it is of
tremendous importance to both the individual and society.
Allergic contact dermatitis may appear at any age. It is increasingly being looked
for and recognised in childhood. It is probably equally common in the general and
atopic populations, and a history of concomitant or family allergy is of no help.
Sensitivity to nickel is approximately 10% in women.
The interval between exposure to the causative agent and the manifestations of symptoms
is usually 12 to 48 hours (A Delayed hypersensitivity reaction). The incubation
period (ie. the time between initial exposure to the agent and the development of
skin sensitivity) may be as short as 2 or 3 days in the case of strong sensitisers
such as poison ivy, or as long as several years for a weak sensitiser such as chromate.
Once sensitivity is established, it generally persists for many years (sometimes
The clinical appearance of allergic contact dermatitis depends upon the stage at
which the patient presents. In the acute stage, redness, bumps and blisters predominate.
Swelling of the eyelids is common when the face is affected. This can be mistaken
for angioedema seen in acute allergic reactions associated with hives, as seen in
food and drug allergy. In the chronic stage few bumps or blisters are seen, and
thickening and scaling predominate.
Skin areas vary in their susceptibility to sensitisation by contact allergens. The
eyelids, neck, and genitalia are amongst the most easily sensitised areas. The palms,
soles and scalp are more resistant, since the skin is thicker. Pressure, friction
and perspiration seems to promote the process of sensitisation, and a tissue that
is already irritated, inflamed, or infected has heightened susceptibility.
Often the location of the dermatitis is the place at which the patient's skin surface
made direct contact with the allergen.
We believe that your skin disease may be related to contact with chemicals in your
environment. This is called allergic contact dermatitis.
The only way to obtain proof of allergic contact dermatitis is by patch testing.
This is different from skin prick testing (which gives a positive response in 15
minutes) in that it is a delayed hypersensitivity response (positive response in
about 48 hours).
Chemicals will be taped to your back in small chambers. The skin will not be broken.
The "patches" stay in place for 48 hours. You cannot shower or do any
work or exercise that will wet or loosen the patches.
The "patches" will be removed, and a reading will be done after 2 days.
The patch sites will be marked, and you may be asked to return for a final reading
on another day. Between the two readings you can bathe, but you may not wash your
You may develop itching under the patches. If it becomes very severe or if you develop
pain, you should contact the clinic. If you are unable to contact the clinic, have
someone carefully remove the painful patch. Try not to disturb the other patches.
You may develop blisters at the positive sites, and very rarely prolonged reactions
or even scars may develop at such sites.
You will be tested for your response to common chemicals. If you believe that any
agent or product even a medication worsen your problem, please bring it with you
(and the container with the ingredient list) when you come for patch testing.
You should not be tested if you are taking cortisone pills (eg. prednisone), have
had a cortisone injection, are applying cortisone to your back, or have had sun
on your back recently. Please tell the nurse or doctor if any of these have occurred.
Please tell the doctor if you are pregnant. Please call if you have any problems.
Please ask if you have any questions.
Your tests may be completely negative. This probably means that a contact allergy
is not the cause of your skin problem. The test is not infallible, however, and
an allergy may be missed. Retesting in the future may be indicated.
3. Hives (Acute Urticaria)
Hives are itchy skin rashes with raised weals of different sizes. Sometimes they
look like mosquito bites. They are sometimes referred to as urticaria. They may
appear a few at a time or they may spread over the whole body. Hives tend to come
and go and change places over the body. They last from minutes to days or may recur
in crops for a period of weeks or months in different areas. If hives last for more
than six weeks they are called chronic urticaria. Hives lasting less than six weeks
are known as acute urticaria.
Hives may affect the deeper layers of the skin and cause swelling. This is called
angioedema. Hives and angioedema may appear together or separately.
Hives can be caused by foods (especially milk, eggs, wheat, seafood, & peanuts),
drugs like aspirin and penicillin, infections and inhaled substances like cat hair
and house dust mites. Physical agents like cold, heat, sunlight, direct pressure,
vibration and rubbing can also cause hives in some people. Insects like mosquitos,
bed bugs and fleas can produce small crops of small itchy swellings on exposed parts
of the body, especially the lower extremities in children. These may be a form of
hives called papular urticaria.