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U N I T 1 3
Integumentary Function
melanocytes, or, in some cases, melanocytes that no
longer produce melanin. Although there are many treat-
ment regimens for vitiligo, none is curative. Self-tanning
lotions, skin stains, and cosmetics are used for cam-
ouflage. Micropigmentation (tattooing) has been done
on smaller, recalcitrant areas, but it is often difficult to
attain a correct color match. If extensive skin surfaces
are involved, the treatment may be reversed and the pig-
mented areas bleached to match the remainder of the
skin color. A melanocytotoxic agent is used to remove
remaining melanocytes from skin areas.
Melasma
is a disorder characterized by darkened mac-
ules on the face. It is common in all skin types, but most
prominent in brown-skinned people from Asia, India, and
South America. It occurs in men but is more common
in women, particularly during pregnancy or while using
oral contraceptives. It may or may not resolve after giving
birth or discontinuing hormonal birth control. Melasma
is exacerbated by sun exposure. Treatment measures are
palliative, mostly consisting of limiting exposure to the
sun and using sunscreens. Bleaching agents containing 2%
to 4% hydroquinone are standard treatments.
Pruritus
Pruritus is an unpleasant sensation of itch leading to the
desire to scratch. Symptoms of pruritus range from mild
to so severe that it interrupts sleep and the general qual-
ity of life. While pruritus most commonly occurs in skin
disorders, it may also occur with systemic disorders, such
as chronic kidney disease, diabetes, and biliary disease.
Pruritus is multidimensional and has been classified into
four types: (a) pruritoceptive (generated in the skin: bug
bites), (b) neurogenic (generated in the central nervous
system: cholestasis), (c) neuropathic (due to lesions in the
central nervous system blocking normal responses), and
(d) psychogenic (emotional or stress related).
Pruritus originates within the skin’s free nerve end-
ings, is carried by small myelinated type C nerve fibers to
the dorsal horn of the spinal cord, and is then transmit-
ted to the somatosensory cortex through the spinotha-
lamic tract (see Chapter 35). Many chemicals have been
found to produce the itch sensation, including histamine,
serotonin, and cytokines. Substances such as bradykinin
and bile salts act locally to stimulate the itch sensation.
Prostaglandins are modulators of the itch response, low-
ering the threshold for other mediators. Opioids produce
pruritus in a number of patients who receive them while
narcotic antagonists have been used successfully to relieve
pruritus. Regardless of cause, pruritus is often exacer-
bated by skin inflammation, dry or hot ambient tempera-
tures, skin vasodilation, and psychological stressors.
Scratching, the well-known response to itch, is a spi-
nal reflex response that to varying degrees can be con-
trolled by the individual. While providing momentary
relief, scratching increases inflammation and stimulates
nerve endings, leading to more itching and scratching.
Repeated scratching also causes undesirable changes in
the skin such as lichenification. Successful treatment of
pruritus requires interruption of this cycle.
The focus of treatment measures for pruritus can be
grouped into two categories: specific and nonspecific.
Specific treatment involves finding and correcting the
underlying disorder, thereby eliminating the itch sensa-
tion. Nonspecific measures involve the use of measures
to relieve the itch sensation and prevent complications
that arise from intense and persistent scratching.
Measures such as using the entire hand to rub over
large areas and keeping the fingernails trimmed often
can relieve itch and prevent skin damage. Self-limited
or seasonal cases of pruritus may respond to treatment
measures such as moisturizing lotions, bath oils, and the
use of humidifiers. Because vasodilation tends to increase
itching, cold applications may provide relief. Cool show-
ers before bed, light sleepwear, and cool home tempera-
tures also may be helpful. Also helpful can be cooling
over-the-counter anti-itch agents containing menthol,
camphor, or phenol. These substances stimulate nerve
fibers that transmit the sensation of cold, thereby mask-
ing the itch sensation. Mild cutaneous disorders, such
as bug bites, are mediated by histamine; therefore, topi-
cal antihistamines tend to be the treatment of choice.
Topical corticosteroids are effective as antipruritics, par-
ticularly when used for urticaria (hives) or insect bites.
However, because most cases of pruritus are not his-
tamine related, their management should be directed
at the underlying cause. For example, systemic antihis-
tamines and corticosteroids may be indicated for per-
sons with severe pruritus or atopic dermatitis. Topical
capsaicin cream and topical aspirin have been used for
localized chronic pruritic disorders. Other modalities
that have been used for pruritus with varying degrees of
success are phototherapy, acupuncture, antidepressant
medications, behavior modification, and alternative
therapies (herbal, nutritional, and reflex therapies). In
persons with pruritus due to a systemic cause, itching
gradually recedes as the primary condition improves.
Dry Skin
Dry skin, also called
xerosis,
may be a natural occur-
rence, as in the drying of skin associated with aging, or
it may be symptomatic of an underlying systemic disease
or skin disorder such as contact dermatitis. Most cases
of dry skin are caused by dehydration of the stratum
corneum. The effects of aging on skin dryness include a
change in the composition of sebaceous gland secretions
and a decrease in the secretion of moisture from the
sweat glands. Aging is also accompanied by a decrease
in skin capillaries as well as a flattening of the dermal
rete ridges, resulting in less surface area for exchange of
fluids between the dermis, epidermis, and skin surface.
Dry skin appears rough and scaly; there may be
increased wrinkles or lines. Persons with dry skin often
experience severe pruritus, most commonly of the
extremities, back, abdomen, or waist. They may resort
to scratching, resulting in cracking, fissuring, and a
number of other skin maladies.
Moisturizing agents are the cornerstone of treatment
for dry skin. These agents exert their effects by repair-
ing the skin barrier, increasing the water content of the
