Human scabies is caused by an
infestation of the skin by the human
itch mite (Sarcoptes scabiei var.
hominis). The microscopic scabies
mite burrows into the upper layer of
the skin where it lives and lays its
eggs. The most common symptoms
of scabies are intense itching and a
pimple-like skin rash. The scabies
mite usually is spread by direct,
prolonged, skin-to-skin contact with a
person who has scabies.
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Scabies occurs worldwide and affects people of all races and social classes.
Scabies can spread rapidly under crowded conditions where close body contact is
frequent. Institutions such as nursing homes, extended-care facilities, and prisons
are often sites of scabies outbreaks.

Causal Agent:

Sarcoptes scabiei var. hominis, the human itch mite, is in the arthropod class
Arachnida, subclass Acari, family Sarcoptidae.  The mites burrow into the upper
layer of the skin but never below the stratum corneum.  The burrows appear as tiny
raised serpentine lines that are grayish or skin-colored and can be a centimeter or
more in length.  Other races of scabies mites may cause infestations in other
mammals, such as domestic cats, dogs, pigs, and horses.  It should be noted that
races of mites found on other animals may cause a self-limited infestation in
humans with temporary itching due to dermatitis; however they do not multiply on
the human host.

Sarcoptes scabiei undergoes four stages in its life cycle:  egg, larva, nymph and
adult.  Females deposit 2-3 eggs per day as they burrow under the skin .  Eggs are
oval and 0.10 to 0.15 mm in length  and hatch in 3 to 4 days.  After the eggs hatch,
the larvae migrate to the skin surface and burrow into the intact stratum corneum to
construct almost invisible, short burrows called molting pouches.  The larval stage,
which emerges from the eggs, has only 3 pairs of legs  and lasts about 3 to 4 days.  
After the larvae molt, the resulting nymphs have 4 pairs of legs .  This form molts
into slightly larger nymphs before molting into adults.  Larvae and nymphs may
often be found in molting pouches or in hair follicles and look similar to adults, only
smaller.  Adults are round, sac-like eyeless mites.  Females are 0.30 to 0.45 mm
long and 0.25 to 0.35 mm wide, and males are slightly more than half that size.  
Mating occurs after the active male penetrates the molting pouch of the adult female
.  Mating takes place only once and leaves the female fertile for the rest of her life.  
Impregnated females leave their molting pouches and wander on the surface of the
skin until they find a suitable site for a permanent burrow.  While on the skin’s
surface, mites hold onto the skin using sucker-like pulvilli attached to the two most
anterior pairs of legs.  When the impregnated female mite finds a suitable location, it
begins to make its characteristic serpentine burrow, laying eggs in the process.  
After the impregnated female burrows into the skin, she remains there and
continues to lengthen her burrow and lay eggs for the rest of her life (1-2 months).  
Under the most favorable of conditions, about 10% of her eggs eventually give rise
to adult mites.  Males are rarely seen; they make temporary shallow pits in the skin
to feed until they locate a female’s burrow and mate.

Transmission occurs primarily by the transfer of the impregnated females during
person-to-person, skin-to-skin contact.  Occasionally transmission may occur via
fomites (e.g., bedding or clothing).  Human scabies mites often are found between
the fingers and on the wrists.


When a person is infested with scabies mites the first time, symptoms usually do not
appear for up to two months (2-6 weeks) after being infested; however, an infested
person still can spread scabies during this time even though he/she does not have

If a person has had scabies before, symptoms appear much sooner (1-4 days) after
exposure. An infested person can transmit scabies, even if they do not have
symptoms, until they are successfully treated and the mites and eggs are destroyed.

Common Symptoms

The most common symptoms of scabies, itching and a skin rash, are caused by
sensitization (a type of “allergic” reaction) to the proteins and feces of the parasite.
Severe itching (pruritus), especially at night, is the earliest and most common
symptom of scabies. A pimple-like (papular) itchy (pruritic) “scabies rash” is also
common. Itching and rash may affect much of the body or be limited to common
sites such as: between the fingers, wrist, elbow, armpit, penis, nipple, waist,
buttocks, shoulder blades.

The head, face, neck, palms, and soles often are involved in infants and very young
children, but usually not adults and older children.

Tiny burrows sometimes are seen on the skin; these are caused by the female
scabies mite tunneling just beneath the surface of the skin. These burrows appear
as tiny raised and crooked (serpiginous) grayish-white or skin-colored lines on the
skin surface. Because mites are often few in number (only 10-15 mites per person),
these burrows may be difficult to find. They are found most often in the webbing
between the fingers, in the skin folds on the wrist, elbow, or knee, and on the penis,
breast, or shoulder blades.

Possible Complications

The intense itching of scabies leads to scratching that can lead to skin sores. The
sores sometimes become infected with bacteria on the skin, such as
Staphylococcus aureus or beta-hemolytic streptococci. Sometimes the bacterial skin
infection can lead an inflammation of the kidneys called post-streptococcal

Crusted (Norwegian) scabies

Crusted (Norwegian) scabies is a severe form of scabies that can affect the elderly,
persons who are immunocompromised, or persons who have conditions that
prevent them from itching and/or scratching (spinal cord injury, paralysis, loss of
sensation, mental debility). Crusted scabies is characterized by vesicles and thick
crusts over the skin that can contain many mites. Itching (pruritus) may be absent in
crusted scabies because of a patient’s altered immune status or neurological
condition. Because they are infested with large numbers of mites (up to 2 million),
persons with crusted scabies are very contagious. Persons with crusted scabies
may not show the usual signs and symptoms of scabies such as the characteristic
rash or itching (pruritus).


In addition to the infested person, treatment also is recommended for household
members and sexual contacts, particularly those who have had prolonged direct
skin-to-skin contact with the infested person. Both sexual and close personal
contacts who have had direct prolonged skin-to-skin contact with an infested person
within the preceding month should be examined and treated. All persons should be
treated at the same time to prevent reinfestation.

Products used to treat scabies are called scabicides because they kill scabies
mites; some also kill mite eggs. Scabicides used to treat human scabies are
available only with a doctor’s prescription. No “over-the-counter” (non-prescription)
products have been tested and approved to treat scabies. The instructions
contained in the box or printed on the label always should be followed carefully.
Always contact a doctor or pharmacist if unsure how to use a particular medicine.

Scabicide lotion or cream should be applied to all areas of the body from the neck
down to the feet and toes. In addition, when treating infants and young children,
scabicide lotion or cream also should be applied to their entire head and neck
because scabies can affect their face, scalp, and neck, as well as the rest of their
body. The lotion or cream should be applied to a clean body and left on for the
recommended time before washing it off. Clean clothing should be worn after

Bedding, clothing, and towels used by infested persons or their household, sexual,
and close contacts (as defined above) anytime during the three days before
treatment should be decontaminated by washing in hot water and drying in a hot
dryer, by dry-cleaning, or by sealing in a plastic bag for at least 72 hours. Scabies
mites generally do not survive more than 2 to 3 days away from human skin.

Because the symptoms of scabies are due to a hypersensitivity reaction (allergy) to
mites and their feces (scybala), itching still may continue for several weeks after
treatment even if all the mites and eggs are killed. If itching still is present more than
2 to 4 weeks after treatment or if new burrows or pimple-like rash lesions continue to
appear, retreatment may be necessary.

Skin sores that become infected should be treated with an appropriate antibiotic
prescribed by a doctor.

Medications Used to Treat Scabies

Products used to kill scabies mites are called scabicides. Scabicides used to treat
human scabies are available only with a doctor’s prescription. No “over-the-counter”
(non-prescription) products have been tested and approved to treat human scabies.

The instructions contained in the box or printed on the label always should be
followed carefully. Always contact a doctor or pharmacist if unsure how to use a
particular medicine.