What Causes Scabies?

Medically reviewed by Leah Ansell, MD

Scabies is an intensely itchy skin condition caused by a parasite called Sarcoptes scabiei found all over the world. Scabies is passed through skin-to-skin contact (including sexual contact) but can also be spread through bedding or clothing that has been infested with the burrowing mite.

While anyone can get scabies, certain people are at greater risk, including those who live in crowded spaces or are caregivers in nursing homes.

This article explains how scabies is—and isn't—spread, including the risk factors that place you at greater risk of infestation.

Cause of Scabies

Scabies is caused by the female Sarcoptes scabiei mite. The female mite burrows deep into the skin of a human host, laying eggs that eventually hatch as larvae. The hatching triggers symptoms like pruritus (itchiness) as well as a papular (pimple-like) rash.

The symptoms are aggravated by the body's natural immune response, during which inflammation intensifies the itchiness, redness, and swelling of the skin.

The female Sarcoptes scabiei mite lives for around 8 weeks and can continue to lay eggs the entire time. As the larvae mature and feed off human tissues, they can also start to mate and lay eggs, perpetuating and expanding the infestation.

Following the initial exposure to the female Sarcoptes scabiei mite, symptoms of scabies can take anywhere from 4 to 8 weeks to develop.

A scabies infestation can sometimes affect large portions of the body or be limited to the wrists, elbows, armpits, belt-line, buttocks, or the webbing between fingers.

Scabies can also affect the head, face, neck, palms, and soles of infants and toddlers, but usually not adults or older children.

How Scabies Is Spread

Scabies can be transmitted directly from person to person or indirectly through contact with contaminated items (referred to as fomite transmission).

Skin-to-Skin Contact

Scabies is most often passed through prolonged skin-to-skin contact with someone with scabies. Because it can take weeks for symptoms to develop, a person with scabies may not even be aware that they are a carrier.

In adults, scabies is often transmitted by sexual partners. With that said, family members and people who live together can easily transmit the mite back and forth to each other.

Contact through professional massage can also potentially transmit the parasite from one person to the next.

Fomite Transmission

A scabies infestation often affects the home as well as households. This includes furniture, bedding, towels, and clothing where Sarcoptes scabiei mites can survive for 2 to 3 days without a human host.

Contact with these items can independently cause scabies. Even if a person is treated for scabies, they can still get reinfected unless these items are properly sanitized.

This can be done by machine-washing bedding, clothing, blankets, and towels in hot water and tumble-drying on the hot cycle.

Items that cannot be washed or dry-cleaned can be decontaminated by isolating them from body contact for at least 72 hours. Vacuuming of furniture and carpets is also recommended.

The fumigation of rooms is not necessary.

Norwegian (Crusted) Scabies

Norwegian scabies is the term used to describe crusted scabies that affects people who are immunocompromised (have a severely weakened immune system). When a person's immune system is impaired, the body is less able to fight infections.

Norwegian scabies most commonly affects:

• People with untreated HIV

• People on chemotherapy

• Organ donor recipients on immunosuppressant drugs

• Adults over 65

• People with leukemia

• People with severe nutritional deficiency

"Regular" scabies may involve anywhere from 12 to 20 mites on the body at any one time. Norwegian scabies may involve more than 1,000 mites.

Because of this, Norweigan scabies is easier to pass simply by virtue of their numbers. This includes the transmission of scabies through infested clothes, bedding, and towels.

Related: How Scabies Is Diagnosed

How Scabies Isn't Spread

Scabies is not passed through casual contact, such as a quick handshake or hug. Transmission of Sarcoptes scabiei generally requires prolonged exposure.

Some people associate scabies with a lack of hygiene. The simple fact is that poor hygiene does not cause scabies, and cleanliness does not prevent scabies. This is because the mites live deep within the skin and cannot be washed off.

Having scabies simply means that you have been in close contact with someone—or something—that has scabies.

What About Pets?

While pets can spread certain parasites to humans, Sarcoptes scabiei is not one of them. While there have been isolated reports of transmission from pet pigs to humans, the risk of this occurring is considered low to unlikely.

Who Gets Scabies?

Certain people are at greater risk of scabies than others due to their living situation or their job.

Environment

Scabies is known to spread among people who live in crowded quarters. Outbreaks often occur in daycare settings, military quarters, prisons, and homeless shelters where vulnerable people are packed into a small space.

Severe outbreaks are possible in nursing homes because residents are older and more likely to get Norwegian scabies.

Occupations

Caregivers in shelters and nursing homes can get scabies even if personal hygiene is maintained. Sex workers are vulnerable to transmission as are people who engage in non-sexual touch, such as massage therapists.

Wearing gloves and other protective coverings in these settings may decrease the chances of getting or passing scabies.

Summary

Scabies is caused when the female Sarcoptes scabiei mite burrows into your skin and lays eggs. Scabies is most commonly passed through prolonged skin-to-skin contact but can also be spread through infested bedding, clothing, furniture, or towels.

People who live in crowded quarters or are caregivers in places like nursing homes are at greater risk. People who are older or are immunocompromised are also more likely to get a severe form of scabies, known as Norwegian (crusted) scabies.

Frequently Asked Questions

Can I get scabies while working in my garden?

No. Scabies is predominately transmitted via prolonged, skin-to-skin contact with someone who has scabies. If you develop a rash that resembles scabies after gardening, doing yard work, or spending time outdoors, it's possible that you've been bitten by chiggers instead.

Do I have to get rid of my mattress if I have scabies?

No, but it's a good idea to clean your mattress. Strip off all bedding and vacuum both sides of the mattress thoroughly (using the crevice attachment to get between seams and folds). Steam cleaning is not necessary.