Scabies is a contagious skin infestation caused by a microscopic eight-legged mite, Sarcoptes scabiei var. hominis. This tiny parasite burrows into the upper layer of human skin to live, feed, and lay eggs, triggering an intense allergic reaction in the host. The condition is a common dermatological problem found across the world, affecting anyone regardless of hygiene. Transmission generally requires prolonged, direct skin-to-skin contact, meaning a quick hug or handshake is unlikely to result in infestation.
How Scabies Spreads Through Contact
The Sarcoptes scabiei mite cannot jump or fly, requiring physical proximity for transfer. Transmission typically occurs through extended skin-to-skin contact, often defined as lasting 10 to 20 minutes or longer. This extended contact is needed for the mite to move, which is why spread is most common among sexual partners and household members who share a bed or spend significant time in close physical proximity.
Casual, brief contact, such as a quick hug or a handshake, is not considered a risk factor for transmitting typical scabies. Mites are usually found in low numbers, averaging only 10 to 15 adult mites on an infested person, making indirect transfer rare. Mites can survive off a human host for two to three days, so indirect spread through shared clothing, towels, or bedding is possible, but it is less common than direct contact.
A much more contagious form is crusted scabies, sometimes called Norwegian scabies, which develops in individuals with a weakened immune system. People with crusted scabies harbor thousands of mites, making them highly infectious. In these cases, transmission can occur more easily from brief direct contact or indirectly from contaminated items like furniture and clothing. This form requires more aggressive treatment and environmental cleaning due to the high mite load.
Identifying the Signs of Scabies Infestation
The most prominent sign of a scabies infestation is intense itching (pruritus), which often worsens at night or after a hot shower. This severe itching is an allergic reaction to the mites, their eggs, and their feces. For a person who has never been infected before, symptoms may not appear until four to six weeks after the initial infestation, although they are contagious during this period.
The skin reaction includes a rash of tiny blisters, bumps, or pimple-like lesions. The most characteristic sign is the presence of tiny, raised, grayish-white lines called burrows, which represent the tunnel the mite creates just beneath the skin surface. Common sites include the webbing between the fingers, the inner surfaces of the wrists and elbows, the armpits, the waistline, and the genitals.
Infants and young children may exhibit a more widespread rash, sometimes including the palms, soles of the feet, and the scalp, areas less commonly affected in adults. If a person has had scabies previously, the immune response is faster, and symptoms can appear sooner, usually within one to four days of re-exposure. Scratching the rash can lead to secondary bacterial skin infections, presenting as sores or crusts.
Treatment Protocols and Environmental Cleaning
Treatment for scabies involves a two-part strategy: eradicating the mites on the person and decontaminating the environment. Mite-killing medications, called scabicides, require a prescription from a healthcare provider. The most common topical treatment is a 5% permethrin cream, which is applied to the entire body, from the neck down to the soles of the feet, and washed off after the recommended time.
Oral medication, such as ivermectin, may be prescribed, especially for those with crusted scabies or when topical treatments are difficult to apply. Since medication does not kill the eggs, a second treatment is often required one week later to eliminate newly hatched mites. All close personal contacts, including household members, must be treated simultaneously, even if they do not yet show symptoms, to prevent re-infestation.
Environmental cleaning focuses on items used by the infested person during the three days before treatment. All clothing, bedding, and towels should be machine-washed using hot water and dried in a hot dryer, as temperatures above 122°F for at least 10 minutes will kill mites and eggs. Items that cannot be washed or dry-cleaned can be sealed in a plastic bag for a minimum of 72 hours to starve the mites.