tions that allow scratching. Because the cause of
prurigo, also called prurigo nodularis, remains
unknown, dermatologists do not know whether
the lesions develop in response to scratching or
whether the itching of the lesions establishes the
need to scratch. Whichever is the case, one per-
petuates the other. The lesions eventually develop
coarse, scaly surfaces. The intense itching drives
many people to scratch the lesions until they
bleed, which causes scabs to develop. Lesions that
heal often leave white scars. An outbreak of
lesions may extend over months or even years.
Prurigo is sometimes associated with LIVERdis-
ease, KIDNEY disease, HIV/AIDS, atopic DERMATITIS,
GENERALIZED ANXIETY DISORDER (GAD), and also
DEPRESSION. Most people who develop prurigo are
middle-age or older, though occasionally the con-
dition occurs in young people. The diagnostic
pathway may include biopsy to rule out other
causes for the lesions. Treatment generally incor-
porates topical CORTICOSTEROID MEDICATIONS and
topical or oralANTIHISTAMINE MEDICATIONS to sub-
due the itching. The dermatologist may choose
to inject large or recurrent lesions with a corti-
costeroid medication. Some people who have
prurigo benefit from psoralen plus ultraviolet A
(PUVA) PHOTOTHERAPYor cryotherapy (freezing),
which destroys the lesions and allows the skin to
heal.
See also LESION; LICHEN SIMPLEX CHRONICUS; NOD-
ULE; PAPULE; PRURITUS; SCAR.
pruritus The clinical term for itching, especially
itching that engenders the uncontrollable urge to
scratch. Pruritus is a symptom of innumerable
health conditions and may be localized (confined
to a specific area or to lesions) or generalized
(widespread, involving much of the SKIN’s sur-
face). The skin may appear reddened (erythema),
swollen (edema) or otherwise irritated, or may
show no reason for the itching.
The physiologic mechanism of itching is similar
to, though distinctive from, that of PAIN. The NERVE
cells, called nociceptors, that send itch signals to
the BRAINare scattered throughout the epidermis
and upper layer of the dermis. Irritants that con-
tact the epidermal and dermal layers of skin can
arouse the nociceptors, coming from the external
surface of the skin (such as from lesions that form
on the skin) or from within (such as the accumu-
lation of BILIRUBIN, which accounts for the itching
that accompanies JAUNDICE). HISTAMINE, which the
IMMUNE SYSTEMreleases during a HYPERSENSITIVITY
REACTION(allergy or ASTHMA), is among the internal
stimuli that activate these nociceptors.
The response of scratching is a REFLEXthat the
autonomic NERVOUS SYSTEMgenerates in response
to itch signals. Researchers theorize that scratch-
ing activates a mild pain response that overrides
the itch response. Pain and itch appear to use
many of the same nociceptors, and pain seems to
be the more dominant stimulus. However, many
factors contribute to the experience of itching aspruritus 187HEALTH CONDITIONS ASSOCIATED WITH PRURITUSadverse DRUGreaction ANEMIA BULLOUS PEMPHIGOID
CANDIDIASIS CHICKENPOX CHLAMYDIA
CIRRHOSIS CONJUNCTIVITIS DERMATITIS
DIABETES drySKIN FOLLICULITIS
GENITAL HERPES HEPATITIS HERPES SIMPLEX
HYPERTHROIDISM ICHTHYOSIS IMPETIGO
JAUNDICE LEUKEMIA LICHEN PLANUS
LICHEN SIMPLEX CHRONICUS LYMPHOMA MEASLES
MILIARIA parasitic infections PEDICULOSIS
PEMPHIGUS PILONIDAL DISEASE PITYRIASIS
POLYCYTHEMIA VERA PRIMARY BILIARY CIRRHOSIS PRIMARY SCLEROSING CHOLANGITIS
PRURIGO PSORIASIS RENAL FAILURE
RUBELLA SCABIES TINEA INFECTIONS
URTICARIA VAGINITIS VULVODYNIA