The arthropod Sarcoptes scabiei var hominis causes an intensely pruritic and highly contagious skin infestation. Scabies in adults frequently is sexually acquired, although scabies in children usually is not. The first time a person is infested with S scabiei, sensitization can take several weeks to develop; however, pruritus may occur within 24 hours after a subsequent reinfestation. 
See When Bugs Feast: What's Causing that Itch?, a Critical Images slideshow, to help identify various skin reactions, recognize potential comorbidities, and select treatment options.
See the list below:
Ivermectin 200 mcg/kg PO once, repeated at 2wk if necessary; not recommended for pregnant or lactating patients, and safety in children who weigh < 15 kg has not been determined (off-label use) or
Crotamiton 10% lotion or cream: Apply from the neck down on 2 consecutive nights; thoroughly massage into the skin of the whole body from the chin down, paying particular attention to all folds and creases; a second application is advisable 24h later; wash off 24h after second application; considered less effective than permethrin or
Lindane* 1% lotion or cream: Apply 30-60 mL from the neck down; wash off after 8-12h; no residual activity; increasing drug resistance; contraindicated in infants, children, women who are pregnant or nursing, elderly, persons with seizure disorders, persons who weigh < 110lb, and persons with itching/sores where lotion will be applied
*NOTE: Lindane is potentially neurotoxic and is considered a second-line drug for scabies in the event of failure of other medicines. The World Health Organization classifies lindane as "Moderately Hazardous". Since 2009, it is restricted and regulated under the Rotterdam Convention. It is not available in certain states such as California, although there is a specific exemption to the general ban, allowing it to be used as a second-line pharmaceutical treatment for lice and scabies in some places.
Particular attention must be given to the fingernails of these patients, and recommendations include advising patients to trim fingernails.
Treatment of fellow household members and close contacts, as well as washing clothing, bedding, and towels in warm or hot water, is recommended.
Items that cannot be washed can alternatively be isolated from use for 3 days.
Infested individuals may be asymptomatic for up to 6 weeks but are able to transmit infestation; symptomatic individuals may harbor less than 15 mites, making the location of burrows difficult.
Norwegian scabies is a severe infestation with crusted lesions, typically in elderly and immunocompromised individuals; it is highly contagious, with individuals harboring millions of mites.
Symptomatic individuals in an institutional setting indicate an infestation lasting several months; surveillance among institutionalized persons and staff, as well as control (ie, handwashing, avoidance of skin-to-skin contact with cases), should be put in place.
The US Centers for Disease Control and Prevention offer the following suggested guidelines for the treatment of scabies  :
Treatment should be given to both the infested person a nd to household members and sexual contacts, particularly those who have had prolonged direct skin-to-skin contact with the infested person.
All persons should be treated at the same time to prevent reinfestation.
Bedding, clothing, and towels used by infested persons or close contacts anytime during the 3 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 2-3 days away from human skin.
Use of insecticide sprays and fumigants is not recommended.
Scabicides are available only with a prescription. No over-the-counter (nonprescription) products have been tested and approved to treat scabies.
For classic scabies, one or more of the following may be used: permethrin cream 5%, crotamiton lotion 10% and crotamiton cream 10%, sulfur (5-10%) ointment, lindane lotion 1%, or ivermectin.
For crusted scabies, both oral and topical agents should be used together.