Causes and Risk Factors of Scabies

The parasitic mite that causes scabiesSarcoptes scabieiis found all over the world and in a variety of settings. It is passed from person to person through skin-to-skin contact, which is often sexual contact, but certainly not always. Less often, a person can get scabies from contact with an object housing the mite, like bedding or clothing. The mite's life cycle depends on humans, and it cannot survive for longer than a few days outside a human "host." While anyone can get scabies, certain individuals—like those who live in crowded areas, have a greater risk.

Common Causes

scabies causes
Illustration by Joshua Seong. © Verywell, 2018.

There is only one actual cause of scabies, and that is mite infestation; the adult female is the culprit. That said, it's skin-to-skin contact with someone who has the mite that typically results in scabies transmission. That can happen in a couple of different ways.

The Mite

The female mite burrows deep in the skin of an infected human host, laying eggs that hatch as larvae. Multiple larvae mature, causing symptoms of itching and rash as the infected human mounts an immune reaction, which exacerbates the symptoms and inflammation.

The adult form of the larvae is able to mate as they live and feed on the human host's body. A pregnant female mite may travel through close human contact with another person, where she can then start the whole infectious process all over again. 

Close Contact

Close and prolonged skin contact with someone who has scabies is most often to blame. Usually, close family members and people who live together easily transmit the infection to one another. In adults, scabies is often (though not exclusively) transmitted by sexual partners.

Scabies is especially known to spread in crowded conditions. Outbreaks may occur in daycare settings, nursing homes, military quarters, prisons, and in shelters, for example. In these situations, re-infection often occurs as infected individuals can pass the mite back to those who already had and were treated for scabies. Re-infection can also occur due to contaminated blankets and other items. 

Contact through professional massage can even spread the infection. Casual contact, such as a handshake, is not usually the source of scabies infection.

Contaminated Items

Households and residential facilities themselves can be infested with scabies. The mite can live on furniture, bedding, towels, and clothing for several days, causing transmission of the infection. However, this happens only when someone has a very severe infection.

Myths: Busted

Some incorrectly associate scabies with a lack of hygiene. Cleanliness does not prevent scabies, as the parasitic mite lives in deep layers of the skin and, therefore, cannot be washed off. Likewise, having scabies does not mean that a person is "dirty." Instead, it means that a person has simply been in close contact with someone who or something that has the infection.

It's also important to know that having been treated for scabies once doesn't mean you can't get it again.

Health Risk Factors

While getting scabies and developing the usual form of the infection can happen to anyone, Norwegian (crusted) scabies is more likely to occur in people whose immune systems are not optimal due to factors such as HIV infection, leukemia, chemotherapy treatment, treatment with other immunosuppressive medications, or severe nutritional deficiency.

This is a more aggressive form of the infection. Most scabies cases involve a total of 12 to 20 mites in the body; crusted scabies may involve more than 1,000 mites.

Lifestyle Risk Factors

These choices or circumstances can increase the odds that you will be exposed to scabies or that it will be transmitted.

Occupation

Caregivers who come into close contact with people, such as in hospital setting, may acquire the infection, even if good hygiene is practiced. Wearing gloves or other protective covering may decrease the chances of catching the infection in these settings.

Environment

If you live or spend a lot of time in cramped quarters, like those mentioned above, or have been exposed to contaminated bedding or clothes for a prolonged period of, you may contract scabies. 

A Word About Pets

While pets can transmit parasitic and bacterial infections to humans, the mite that causes scabies in humans is not typically transmitted to humans through contact with animals (or vice versa). There have been only a few case reports of transmission of scabies from animals to humans, and since these are so few, it is not believed that animals truly pose a risk. 

Was this page helpful?
View Article Sources