causes them to occur, there are no known meas-
ures for preventing them. Any changes in a birth-
mark that has been stable in size and appearance
warrant a doctor’s evaluation to determine
whether the changes signal skin CANCER. Early
detection and treatment are especially crucial for
malignant melanoma, in which a NEVUSbecomes
cancerous, as this cancer can be aggressive and
lethal when untreated. Birthmarks themselves do
not present any risk to overall health.
See also ANGIOMA; GENETIC DISORDERS; LESION.
blister A fluid-filled pocket that develops
between the layers of SKINin response to friction
or pressure. Blisters are most common on the feet
and hands though can develop nearly anywhere
on the body. Blisters often hurt. Their outer layer
of skin is vulnerable to tearing, which allows the
fluid to leak out. Though the blister may then feel
better because there is less pressure, the break in
the skin’s surface gives BACTERIAaccess to the inner
layers of tissue and establishes a risk of INFECTION.
An intact blister usually will heal within three
to five days as the body reabsorbs the fluid and
repairs the damaged skin. A ruptured blister is an
open wound that requires appropriate WOUND
CARE, such as cleansing with mild soap and water
and possibly antibiotic ointment and a bandage.
The most effective treatment for blisters is preven-
tion such as wearing gloves or thick socks and
properly fitting shoes or boots. An area of the skin
that repeatedly forms a blister often develops a
CALLUS, an accumulations of keratocytes, which
increases the skin’s thickness and improves its
ability to withstand friction or pressure.
See also BULLA; CORNS; DECUBITUS ULCER; KERATO-
CYTE.
botulinum therapy Injections of botulinum neu-
rotoxin to selectively paralyze MUSCLEfibers. The
bacterial strain Clostridium botulinumproduces sev-
eral forms of paralytic toxin, some of which can
cause serious or fatal poisoning (BOTULISM) when
ingested. The toxin works by blocking the release
of acetylcholine, a NEUROTRANSMITTERthat facili-
tates NERVEsignals between muscle cells and the
BRAIN. The blockade prevents the muscle cells from
contracting. Botulinum therapy products currently
available in the United States contain a weakened
and purified solution of botulinum neurotoxin A
(Botox) or botulinum neurotoxin B (Myobloc).
Botulinum therapy became therapeutically
acceptable in the United States in 1990 when the
US National Institutes of Health (NIH) issued a
consensus statement outlining the clinical applica-
tions for its use (Clinical Use of Botulinum Toxin
[NIH Consensus Statement]. 1990. November
12–14; 8[8]:1–20). These uses include treatment
for neuromuscular disorders such as DYSTONIA, BLE-
PHAROSPASM, CEREBRAL PALSY, STRABISMUS,TORTICOL-
LIS, MULTIPLE SCLEROSIS, and PARKINSON’S DISEASE, as
well as spasms that result from TRAUMATIC BRAIN
INJURY(TBI) OR SPINAL CORD INJURY.
An outgrowth of these applications was the dis-
covery that botulinum therapy causes SKIN WRIN-
KLESto lessen or disappear. In 2002 the US Food
and Drug Administration (FDA) approved botu-
linum therapy as a cosmetic treatment for fore-
head wrinkles (frown lines). Cosmetic applications
are becoming increasingly common, with many
dermatologists using botulinum therapy to reduce
wrinkles around the eyes and other areas of the
face and body. In 2004 the FDA approved botu-
linum therapy for HYPERHIDROSIS, a disorder of the
SWEAT GLANDSthat results in profuse sweating. The
effects of botulinum therapy last about four to six
months. Risks are slight and may include localized
INFECTIONand temporary weakness of the injected
muscles.
See also BACTERIA; BLEPHAROPLASTY; CHEMICAL
PEEL; RHYTIDOPLASTY.bruise See ECCHYMOSIS.bulla A large (5 millimeters or greater) blister-
like formation, raised and fluid filled, that may
hurt or itch. INFECTION, contact irritants, IMMUNE
RESPONSE, and systemic health conditions may
cause bullae. BullousDERMATITISmay result from
contact with plants such as poison ivy, oak, or
sumac. To determine the cause of bullous erup-
tions, the doctor may biopsy a bulla (remove a
small section for examination under the micro-
scope) or perform tests to look for immune pro-
teins. Tense bullae form in the deeper layers and
are less likely to rupture. Flaccid or loose bullae
form in the superficial layers of the skin and are
fragile, making them more likely to tear.bulla 141