Scabies is a parasitic skin infestation caused by the tiny mite Sarcoptes scabiei, variety hominis. The condition is highly contagious and spreads primarily through prolonged skin-to-skin contact with an infested individual. The female mite burrows into the skin, leading to a delayed allergic reaction that manifests as intense itching and a rash. This characteristic itch often becomes significantly worse at night, disrupting sleep. Scabies requires prescription medication, as it will not resolve on its own.
Where the Scabies Mite Burrows
The scabies mite is biologically suited to live and reproduce within the most superficial layer of human skin, known as the stratum corneum. The female mite uses specialized enzymes to dig serpentine tunnels, or burrows, into this dead, outermost layer of the epidermis. Within these shallow passageways, the female deposits her eggs, laying approximately two to three eggs each day. The resulting lesions are often a reaction to the mite’s presence, eggs, and fecal matter.
In adults, the mites show a strong preference for areas where the skin is thin, creased, and relatively protected. Common sites of infestation include the webs and sides of the fingers, the insides of the wrists and elbows, and the areas around the waistline and belt. Other frequently affected regions are the armpits, the breasts, the buttocks, and the external genitalia. A healthy adult typically hosts a small number of mites, often only 10 to 15 at any given time.
Why Scabies Rarely Involves Hair and Scalp
For most adults, the scalp and areas with thick, dense hair are naturally avoided by the scabies mite during a typical infestation. The mites prefer the softer, less protected skin found in the folds of the body, where the stratum corneum is easier to penetrate for burrowing. The presence of hair follicles and thicker skin layers on the scalp and face makes the burrowing process more difficult for the mites. Therefore, standard treatment protocols for adults often recommend applying medication from the neck down, as the head is usually spared.
A notable exception is a severe form of the condition called Crusted Scabies. This variant occurs in individuals who have a weakened immune system or other underlying conditions that prevent a normal immune response to the mites. In these cases, the mite population explodes, leading to a massive infestation that can number in the millions. This overwhelming number of parasites overcomes the skin’s defenses, causing thick, hyperkeratotic crusts to form, which can include the face, scalp, palms, and soles. Scalp involvement is also more common in infants and very young children, whose skin is thinner than that of older individuals.
Stopping the Spread and Eliminating Mites
Scabies is primarily transmitted through prolonged skin-to-skin contact, meaning that casual contact like a brief handshake is unlikely to spread the mites. Transmission most often occurs among sexual partners and household members, as well as in crowded settings like nursing homes or child care facilities. Successful eradication requires simultaneous treatment of the infested person and all close contacts, even if those contacts are not yet showing symptoms.
Treatment involves prescription topical medications, such as permethrin cream, which is applied to the entire body and left on for a specified period before being washed off. Environmental cleaning is necessary to eliminate any mites that may have fallen off the skin. All clothing, bedding, and towels used by the infested person within the two days before treatment must be washed in hot water and dried on a hot cycle. Items that cannot be washed can be sealed in a plastic bag for at least three days, as mites cannot survive long away from human skin.