Encyclopedia of Health and Medicine

206 The Integumentary System
the IMMUNE RESPONSE draws from the cells of the
skin. They itch, often intensely (PRURITUS), and
may appear and recede in various locations on the
body (migration).
BREATHING difficulties with urticaria
may indicate ANAPHYLAXIS, a life-threatening
hypersensitivity reaction causing
swelling of the airways that requires
emergency medical care.
When urticaria manifests, the first focus is on
subduing the response to relieve the symptoms
and prevent complications. The doctor may
administer an EPINEPHRINE injection to thwart a
hypersensitivity response that appears to be intensifying
or if the urticaria progresses. Most urticaria
responds fairly quickly to ANTIHISTAMINE MEDICA-
TIONS such as diphenhydramine (Benadryl) or
hydroxyzine (Vistaril), which the doctor can
administer by injection for severe urticaria. The
wheals generally retreat within 6 to 8 hours and
are entirely gone in about 36 hours with antihistamine
therapy. Most people recover fully and can
avoid future episodes by avoiding exposure to the
substance that caused the reaction.
Potential complications associated with urticaria
are uncommon though can be life-threatening.
ANGIOEDEMA occurs when fluid accumulates in tissues
other than the skin; most doctors consider it a
progressive form of urticaria. Angioedema can
affect internal structures, causing pressure and
swelling that affects the ability of vital organs to
function. When angioedema affects the airways it
can cause BREATHING difficulties and ANAPHYLAXIS,
the most serious hypersensitivity reaction. These
complications occur only with repeat exposure to
the substance causing the reaction.
Urticaria represents an IMMUNE RESPONSE in
which the immune system releases IMMUNOGLOBU-
LIN E (IgE), which causes mast cells to release HIS-
TAMINE. The histamine draws fluid into the tissues.
Numerous drugs, foods, environmental factors
such as pollen and animal dander, and health conditions
may cause urticaria. It is important to
attempt to identify the causative factor to prevent
recurrences. Hypersensitivity responses, which
people also call allergic reactions, tend to intensify
with repeated exposure to the substance.
A similar release of IgE occurs with chronic
urticaria, as an immune-mediated response
related to serious illnesses that challenge the
immune system such as cancer. AUTOIMMUNE DIS-
ORDERS that affect the connective tissue, such as
SYSTEMIC LUPUS ERYTHEMATOSUS (SLE), AMYLOIDOSIS,
and RHEUMATOID ARTHRITIS, can also cause chronic
urticaria, as can exposure to extreme heat or cold.
As with acute urticaria, treatment for chronic
urticaria first targets symptom relief.
See also DERMATITIS; MAST CELL; WHEAL.