What is urticaria?
Urticaria is a common skin condition. It is also known as
hives. Acute urticaria usually lasts from a few days up to six weeks. Chronic
urticaria, by definition, lasts for more than six weeks. Urticaria normally appears
without obvious triggers (“spontaneous urticaria”). Some patients may observe a
physical stimulus to their symptoms (“inducible urticaria”). Spontaneous and inducible
urticaria may appear in the same patients. A third form of urticaria,
urticarial vasculitis, is uncommon and related to inflammation of blood vessels.
What happens to the skin in urticaria?
The redness and swelling are due to changes in the small
blood vessels of the skin. This leads to increased blood flow to the affected
skin, and excessive fluid moves into the surrounding tissues. Histamine is the
predominant chemical causing these changes and it causes the sensation of itch.
Histamine is released by the mast cell, a special type of immune cell in the
skin. Mast cells release histamine when stimulated.
What does urticaria look like?
Urticaria appears as localised itchy skin swellings and
these raised areas are also called wheals. They can affect any part of the
body. The wheals may be pale, pink or red. They are usually circular, but can appear
in different shapes and sizes. Each wheal usually resolves within 24 hours.
However, new wheals may continue to erupt on other areas. Occasionally, swelling
of the eyelids or lips may occur without any overlying redness of the skin. This
is termed angioedema.
In urticarial vasculitis, the wheals may last for longer than 24
hours. They may also be more painful than itchy, and frequently go away leaving
stains on the skin.
What causes urticaria?
The cause of acute urticaria is frequently not found.
Known triggers include:
- Food such as nuts, strawberries, citrus fruits, egg,
food additives, shellfish. It can occur even if you have eaten it many times
before without any problem.
- Insect bites and stings
- Medicines like penicillin, aspirin, and painkillers
2. Viral infections
3. Contact e.g. chemicals, latex, cosmetics, plants, etc
Like acute urticaria, there is usually no readily identifiable cause
for chronic urticaria. It has been found that some cases of chronic urticaria
may be autoimmune in nature. These patients have antibodies targeting the mast
cells leading to the release of histamine.
Inducible urticarias can be triggered by: physical pressure or friction
on the skin, exercise, changes in skin temperature, vibration and sunlight.
How will it affect me?
Acute urticaria usually resolves after a few days or
weeks. Chronic urticaria may last for months to years. Urticaria causes itch,
which can be very distressing. It may cause significant disruption to the work and
social life. In cases where angioedema is associated with urticaria, the airway
may be affected. This can lead to breathing difficulties and immediate medical
attention may be required.
The majority of people with urticaria are healthy. Urticaria is rarely
associated with an underlying medical condition.
How is urticaria diagnosed?
The diagnosis of urticaria can usually be made from the
history and appearance, or description, of the hives. In the majority of people
no cause can be found. Your doctor may ask you questions to try to identify
In acute urticaria, investigation is usually not necessary. Occasionally,
if an allergic reaction is suspected, a specific blood test for allergic sensitization
(RAST), or a skin prick test may be performed.
Chronic urticaria is rarely caused by allergy; so routine allergy tests
are not necessary. A blood test may be necessary to ensure that there is no
underlying medical condition such as thyroid disease or infection. In a small
percentage of people, foods, colouring agents or preservatives appear to worsen
the urticaria. A food diary may be kept and the suspected substances can be
omitted from the diet to see if the condition improves. These substances can
later be reintroduced to see if it aggravates the urticaria. When inducible urticaria
is suspected, various challenge tests may be performed.
Treatment of urticaria
General measures include avoidance of known physical
triggers, certain medications, alcohol, overtiredness, stress, maintenance of a
cool environment, and light clothing.
Oral antihistamines are the main treatment for urticaria. They relieve
itch and suppress hives. They do not affect the underlying cause of the rash.
Antihistamines may need to be taken intermittently or continuously until the
urticarial disappears. It is recommended that they be taken on a regular basis
if frequent hives are experienced because regular dosing is more effective. The
main side effect of anti-histamines is drowsiness. Non-sedating anti-histamines
are available and these are frequently prescribed, especially during the day.
If patients do not respond to antihistamines, additional medications
such as cyclosporin and omalizumab may be recommended by the doctor.
A short course of oral steroids may sometimes be prescribed in severe
DEDICATED TO EXCELLENCE IN DERMATOLOGY
By National Skin Centre (Singapore)
Copyright (C) 1995 - National Skin Centre (Singapore)