Scabies is a skin infestation caused by the tiny, eight-legged parasitic arachnid, Sarcoptes scabiei var. hominis, commonly called the human itch mite. This microscopic organism is primarily transferred through direct, prolonged skin-to-skin contact with an infested person. Transmission can also occur via contaminated items, or fomites, such as bedding and clothing. Once on a new host, the female mite burrows into the outer skin layer to lay eggs, triggering a severe, itchy reaction. The main concern regarding items like bedding is how long the mite can survive and remain infectious when separated from a human body.
The Scabies Mite: Biology and Host Dependence
The survival of the Sarcoptes scabiei mite is entirely dependent on the human host, making it an obligate parasite that completes its entire life cycle on or in the skin. The adult female requires the host’s skin tissue for food and to create burrows where she deposits eggs. She typically deposits two or three eggs daily during her lifespan, which can last for one to two months on the host.
The human body meets the mite’s physiological needs, specifically the requirement for warmth and moisture. Without these stable, hospitable conditions, the mite cannot reproduce or develop through its life stages (egg, larva, nymph, and adult). This biological necessity dramatically limits its existence once separated from the skin. The mite’s vulnerability outside of the host is a primary factor in preventing reinfestation.
Survival Time Off the Host
Adult scabies mites survive for a relatively short time away from a human host, which is important for environmental cleaning protocols. Under typical indoor conditions, adult mites and nymphs generally do not survive for more than 48 to 72 hours on inanimate objects like bedding, clothing, and furniture. This short survival period is why transmission via fomites is less common than direct skin contact, except in cases of crusted scabies where the mite count is significantly higher.
Survival duration is heavily influenced by ambient temperature and relative humidity. Mites die more rapidly in dry, warm environments because they are susceptible to dehydration. For example, a temperature of 50°C (122°F) will kill mites and their eggs in as little as 10 minutes. Conversely, cooler temperatures and higher humidity levels can extend the mite’s survival closer to the 72-hour limit.
Eradicating Mites from the Environment
Since the mites’ survival off the host is limited to about three days, environmental eradication focuses on killing them quickly with heat or isolating them until they naturally perish. For bedding, towels, and clothing used recently, machine washing in hot water is the most effective method. The water temperature should be set to at least 50°C (122°F) to ensure elimination.
Following the wash cycle, drying the items in a hot dryer is equally important, as high heat for at least 10 to 20 minutes ensures complete elimination. For items that cannot be washed, they should be isolated from human contact. Sealing these items in a closed plastic bag for a minimum of 72 hours is a reliable method to ensure the mites die from starvation and dehydration.
Isolating Non-Washable Items
- Stuffed toys
- Delicate fabrics
- Shoes
- Other non-launderable materials
Upholstered furniture, carpets, and mattresses should be thoroughly vacuumed to remove any mites that may have fallen off the host. After vacuuming, the vacuum bag must be immediately discarded in an outdoor trash receptacle to prevent mites from escaping back into the home. Steam cleaning is another option for mattresses and furniture, as the generated heat kills the mites on contact. Discarding mattresses or fumigating living spaces is unnecessary for typical scabies infestations.