well as to its relief. Scratching is also a conscious
action, and can itself be an irritant that causes
itching. Dermatologic conditions in which the
itch/scratch relationship becomes circular include
LICHEN SIMPLEX CHRONICUSand PRURIGO.
Pruritus is often an early indication of systemic
health conditions such as jaundice or kidney dys-
function, and is a hallmark symptom of dermato-
logic conditions such as PSORIASISand DERMATITIS.
The diagnostic path depends on the complex of
symptoms. Treatment may include topical or sys-
temic ANTIHISTAMINE MEDICATIONSor CORTICOSTEROID
MEDICATIONS and other therapies to resolve the
underlying condition. It is important to resist
the urge to scratch, as scratching further irritates
the skin and may open the pathway for INFECTION.
See also ALLERGY TESTING; AUTOIMMUNE DISORDERS;
LESION; RASH.
pseudofolliculitis barbae A condition in which
large numbers of the hairs in the beard region on
a man’s face grow inward after shaving, causing
irritation and INFLAMMATION. Pseudofolliculitis bar-
bae, sometimes called razor RASHor razor bumps,
occurs most frequently in men whose facial HAIRis
tightly curled, and is particularly common among
African American men. The process of shaving
pulls the hairs before cutting them, allowing the
cut tips to retreat within the hair follicle. When
the facial hair is tightly curled the shaved tips of
the hairs, which are pointed and sharp, turn into
the sides of the follicle. As they grow they punc-
ture the follicle rather than growing out of the fol-
licle’s opening, creating blocked follicles. The
entire beard area often becomes involved, causing
considerable discomfort and difficulty shaving.
The dermatologist can usually diagnose pseudo-
folliculitis barbae on the basis of its appearance,
though may choose to scrape several of the
inflamed papules (bumps) to rule out INFECTION.
Shaving with an electric razor, which does not
pull and cut the hair as much as a blade razor,
may reduce symptoms for some men, though
many men experience irritation and inflammation
regardless of shaving method. When that is the
case, the optimal solution is to stop shaving. Topi-
cal preparations such as benzoyl peroxide lotion or
tretinoin cream are also sometimes helpful,
though may themselves cause SKINirritation.
See also FOLLICULITIS; INGROWN HAIR; PAPULE; TINEA
INFECTIONS.psoriasis A common, chronic SKINcondition in
which the dermis produces keratinocytes at an
accelerated rate. This causes immature ker-
atinocytes, which are still soft, to reach the epider-
mis (the outer layer of the skin). The excess
keratinocytes form lesions, typically scaly plaques,
that itch (PRURITUS) or hurt. The accelerated
turnover of keratinocytes creates an IMMUNE
RESPONSEin the skin that dermatologists refer to as
T-CELLactivation. The immune response produces
INFLAMMATION, the body’s attempt to heal the
plaques. But like the other components of psoria-
sis, the T-cell response is out of control and results
in exacerbating, rather than relieving, the lesions.
Dermatologists believe GENEmutations establish
a predisposition for the accelerations that charac-
terize psoriasis. External or environmental cir-
cumstances such as injury, INFECTION, and stress
then trigger the dysfunctions in the skin that
result in the psoriasis. Psoriasis appears to run in
families, suggesting that the mutated genes are
inherited. Researchers continue to explore the
genetic foundations of psoriasis. Once psoriasis
manifests, it remains in a lifelong pattern of out-
break and REMISSION.
Generally, dermatologists classify five types of
psoriasis. Psoriasis in any of these types can also
cause inflammation of the joints, a form of arthri-
tis called psoriasic arthritis. Dermatologists may
also refer to psoriasis according to the parts of the
body affected, such as palmar-plantar which
affects the palms of the hands and soles of the
feet. About 7 million Americans have psoriasis.
Erythrodermic psoriasisIn erythrodermic pso-
riasis, widespread areas of the skin become red
and scaly, and often swollen. This is the least com-
mon but most severe type of psoriasis. It can
develop from any of the other types of psoriasis.
Flexural psoriasisAlso called inverse psoriasis,
flexural psoriasis forms smooth though itchy
lesions in areas such as the axillae (underarms),
creases of the leg in the groin, under the breasts,
and other skinfold areas. Irritation from rubbing
and sweating exacerbates the lesions.
Guttate psoriasisIn guttate psoriasis, the sec-
ond-most common type of psoriasis, the lesions188 The Integumentary System