Body lice (Pediculus humanus humanus) are parasitic insects that feed exclusively on human blood. Unlike other lice, body lice primarily inhabit the seams and folds of clothing. They move onto the body only several times a day to take a blood meal, then return to the fabric where they spend most of their life cycle. This close association with textiles means the cleanliness of clothing and bedding is directly tied to the risk of infestation. Understanding their survival time off a human host is important for effective control.
Identifying Body Lice vs. Other Types
Human lice are categorized into three distinct types based on their preferred habitat. Body lice are unique because they live and lay eggs almost entirely on clothing fibers, particularly along seams and creases. Head lice (Pediculus humanus capitis) live on the scalp and cement their eggs (nits) firmly to hair shafts. Pubic lice (Pthirus pubis) are generally found in coarse body hair, most often in the pubic region. Because body lice reside in clothing, decontamination of garments is the primary focus for treatment, as the clothing acts as the reservoir for the infestation.
Survival Time Off the Human Host
Adult body lice and nymphs require regular blood meals to survive. Once separated from the warmth and food source of the body, adult lice typically die within 24 to 48 hours due to starvation. Under specific favorable conditions, they might survive for up to 3.5 days, but survival beyond this is uncommon.
The survival of the eggs, or nits, is different, as they are more resistant to environmental changes than the adult louse. Nits take approximately six to nine days to hatch and will not hatch below 74 degrees Fahrenheit. While the adult louse quickly starves, the eggs remain viable on clothing for up to a week. This extended viability means that simply waiting for the adults to die is not sufficient to clear an infestation.
Methods for Decontaminating Infested Items
Eliminating body lice and their eggs relies on using high temperatures or prolonged isolation to interrupt the life cycle. For washable items, machine washing in hot water is highly effective because temperatures above 130 degrees Fahrenheit are lethal to both adult lice and nits. The washing cycle should be followed by machine drying using the high heat setting for at least 20 minutes to ensure complete eradication.
For fabrics that cannot be washed or dried at high heat, isolation is a reliable alternative. These items should be sealed tightly in a plastic bag to prevent lice from escaping and to cut off their access to a blood meal. Sealing the items for a minimum of two weeks is recommended to ensure that any eggs hatch and the resulting nymphs die from starvation. Alternatively, dry cleaning will also kill all stages of the louse.