Lice are tiny parasitic insects that primarily inhabit humans, feeding on blood. They are obligate parasites, meaning they depend entirely on a host for survival. A common concern is how long these creatures can survive once they are no longer on a human body. Understanding their limited off-host lifespan is key to managing and preventing infestations.
Lice Survival Outside the Body
The survival time of lice off a human host varies depending on the type of louse and environmental conditions like temperature and humidity. Lice require warmth and consistent blood meals to thrive. Without these conditions, their survival is severely limited.
Head lice are the most frequently encountered type of louse. Adult head lice perish within 24 to 48 hours when separated from a human host. For example, at 74°F, they may live for two to four days, but at 86°F, their survival drops to one to two days.
Immature head lice, called nymphs, have an even shorter survival time, less than 24 hours, as they are more susceptible to dehydration. The eggs of head lice, known as nits, require the human body’s warmth to hatch. Nits die within about 7 to 10 days if removed from the scalp, as they cannot hatch at or below 68°F.
Body lice have a slightly longer survival period off a host compared to head lice. These lice primarily live in clothing and bedding, only moving to the human body to feed. They can survive off a host for up to a week, though often sooner depending on temperature and humidity. Body lice eggs, or nits, can survive for several weeks, up to 30 days, on clothing or blankets before hatching.
Pubic lice, also known as “crabs,” have a limited survival time off a host, similar to head lice. Adult pubic lice die within 24 to 48 hours. Their eggs hatch within 5 to 10 days.
Environmental Management and Prevention
Given the limited survival time of lice off a human host, especially for head lice, extensive environmental cleaning is often unnecessary. The primary focus should be on treating infested individuals. However, practical steps can address items that may have come into contact with lice.
Machine washing and drying clothing, bedding, and towels used by an infested person during the 2 days before treatment is recommended. Use hot water (at least 130°F/54.4°C) for washing, then dry items on a high heat cycle for at least 20 minutes. Temperatures above 125°F (51.6°C) for 10 minutes are lethal to lice and nits. Allowing time for water to reheat between loads ensures consistent hot temperatures.
For non-washable items like stuffed animals, clothing, or large pillows, dry-clean them or seal them in an airtight plastic bag for at least 2 weeks. This accounts for nit hatching and nymph death due to lack of blood. Vacuuming carpets, rugs, upholstered furniture, and car interiors helps remove any fallen lice. After vacuuming, dispose of the vacuum bag or empty the canister outdoors into a sealed plastic trash bag. Extreme measures like fumigation or chemical sprays are generally not needed, as the risk of reinfestation from lice off a host is low.