Scabies is a common, highly contagious skin condition caused by a tiny, microscopic mite that burrows into the outer layer of human skin. While generally not a serious medical threat, the intense discomfort and ease of spread make understanding its transmission and treatment important. Scabies is not classified as a classical sexually transmitted infection (STI) because sexual activity is not the only way it spreads.
Understanding the Scabies Mite and Transmission Routes
The infestation is caused by the human itch mite, a microscopic parasite that creates shallow tunnels just beneath the skin’s surface to live and lay its eggs. This parasitic activity, and the body’s allergic reaction to the mites and their waste, results in the characteristic symptoms.
Transmission typically requires direct, prolonged skin-to-skin contact with an infested person, which must last for more than a few minutes. This contact duration is necessary for the mite to successfully transfer. Sexual contact often provides this required period of close physical contact, making it a very common route of transmission, especially among young adults. However, the mites can also spread through non-sexual contact, such as extended cuddling or sharing a bed with an infested household member.
Indirect spread through contaminated items like clothing, towels, or bedding is possible but less common with typical scabies, as the mites cannot survive for more than 48 to 72 hours away from a human host.
Crusted Scabies
A special, highly contagious variant called crusted scabies, formerly known as Norwegian scabies, is an exception. People with crusted scabies have a much higher mite burden, sometimes millions, which means they can transmit the infestation through brief contact or even contaminated environmental surfaces. This severe form typically occurs in individuals who are elderly, immunocompromised, or unable to scratch effectively.
Identifying the Signs of Infestation
The most frequent symptom of an infestation is intense itching (pruritus), which often worsens at night or after a warm bath or shower. This severe itching is the body’s allergic reaction to the presence of the mites, their eggs, and their fecal matter within the skin. The rash itself often appears as tiny, pimple-like bumps, blisters, or nodules on the skin.
A specific sign healthcare providers look for is the characteristic scabies burrow, which appears as a tiny, raised, grayish-white line. These burrows and the resulting rash are commonly found in specific areas of the body:
- The webbing between the fingers
- The folds of the wrists and elbows
- The waistline
- The armpits
- The genitals
In a person’s first infestation, symptoms may take four to six weeks to appear due to the delay in the immune system’s sensitization. The infested person can still transmit the mites during this asymptomatic incubation period. If a person has been infested before, symptoms usually appear much sooner, often within one to four days of re-exposure. Diagnosis is typically confirmed through a careful clinical examination, often followed by a skin scraping from a suspected burrow to identify the mites, eggs, or fecal pellets under a microscope.
Effective Treatment and Eradication
Treating a scabies infestation requires prescription medications called scabicides, which are designed to kill the mites and their eggs. The most common treatment is a topical cream, such as 5% permethrin, which is applied to the entire body from the neck down and washed off after a specified period, typically eight to fourteen hours. For more severe cases, or for individuals who cannot use topical treatments, an oral medication like ivermectin may be prescribed, often administered in two doses one week apart.
It is crucial to treat all close personal contacts and household members simultaneously, even if they do not yet show any symptoms, to prevent the cycle of re-infestation. A second application of the medication is usually necessary seven days after the first to kill any mites that have newly hatched from eggs that survived the initial treatment. Because mites can survive briefly off a host, environmental decontamination is also a part of the eradication process.
All clothing, bedding, and towels used by the infested person during the three days prior to treatment must be washed in hot water and dried in a hot dryer. Non-washable items can be sealed in a plastic bag and stored away for at least 72 hours, as the mites will die without a human host during that time. It is common for the itching to persist for two to four weeks even after successful treatment, as the skin continues to react to the dead mites and mite debris.