Head lice are tiny, wingless insects that live exclusively on the human scalp and feed on blood several times a day. They do not transmit disease. A common concern during an infestation is whether these parasites can survive on household items, such as blankets or bedding, and cause re-infestation. Their survival off a human host is highly limited due to their dependence on the scalp’s specific environment.
Survival Limits of Head Lice
Head lice are obligate parasites, meaning they require a human host for survival. An adult louse separated from the scalp will typically survive for no more than 24 to 48 hours. This short survival window is due to the louse’s need for frequent blood meals and the rapid dehydration that occurs away from the warmth and humidity of the human head.
The eggs of the louse, called nits, are tightly cemented to the hair shaft and are even less likely to survive or hatch on bedding. Nits require the stable, warm temperature of the scalp, which is approximately 98.6°F (37°C), to successfully incubate and hatch. If a nit falls onto a blanket, the cooler room temperature makes it highly improbable that it will develop or hatch into a viable louse.
While adult lice die within two days, nits can remain viable for up to 10 days if conditions are favorable. However, the nit is immovably glued to a shed hair and requires warmth to hatch, meaning infestations are not sustained by eggs found on blankets. Elimination efforts should focus primarily on treating the person’s head, not the surrounding environment.
Transmission Routes
Head lice infestations are spread through direct, prolonged head-to-head contact with an infested person. This close proximity allows the adult louse to crawl directly from one hair shaft to another. Lice are unable to jump or fly, and their specialized legs are poorly adapted for walking on flat surfaces, confirming that direct contact is the primary route of transmission.
The risk of contracting lice from inanimate objects, known as fomites, is considered minor by public health organizations. While an adult louse may occasionally crawl onto a blanket or pillowcase, its brief survival time means the blanket does not act as a reservoir for infestation. Rare cases of transfer from objects usually involve items that have been in recent contact with an infested head, such as shared hats, scarves, or hairbrushes.
The short lifespan of the adult louse off the host ensures that blankets and other bedding are not a significant source of re-infestation. Effective management centers on treating the individual and minimizing direct hair contact.
Cleaning and Sanitation of Bedding
Although the risk of transmission from blankets is low, sanitation procedures are important when managing an infestation. Head lice and nits are killed by exposure to high heat, which is the basis for household cleaning recommendations. Any bedding, blankets, or clothing in contact with the infested person’s head in the 48 hours prior to treatment should be addressed.
The most effective non-chemical method for sanitation is machine washing items in hot water, at a temperature of at least 130°F (54.4°C). Following the wash cycle, drying the items on the high-heat setting for a minimum of 20 minutes is also effective at killing both lice and nits. This combination of heat and duration ensures that any adult lice or viable nits are eliminated.
For items that cannot be laundered, such as certain blankets or stuffed toys, sealing them in a plastic bag is an alternative. The sealed item should remain untouched for a minimum of 10 days to ensure that the survival window for adult lice and the full incubation period for nits have been exceeded. Vacuuming furniture and carpets is also a practical measure to remove any shed hairs that may have fallen nits attached.