Head lice (Pediculus humanus capitis) are tiny parasitic insects that live in human hair and feed on blood from the scalp. Infestation is most commonly spread through direct, head-to-head contact, especially among young children. While lice can occasionally transfer to inanimate objects, such as combs and brushes (fomites), the risk of a new infestation starting this way is low due to the insect’s reliance on the human host for survival.
Survival Time of Adult Lice Off the Head
Adult head lice and newly hatched nymphs have an extremely short lifespan once separated from a human host. They rely on human blood for nourishment and require the consistent, warm temperature of the scalp. Without a blood meal and warmth, adult lice typically die within 24 hours of falling onto a surface. Survival may extend up to 48 hours in optimal room conditions, but this is the maximum expected range. Lice quickly dehydrate and starve, making transmission via a brush an improbable source for a new infestation.
Distinction: Survival of Nits (Eggs)
The eggs of head lice, known as nits, behave differently from mobile adult insects when detached. Nits are cemented onto hair strands close to the scalp, requiring the consistent warmth of the scalp (approximately 98.6°F or 37°C) to successfully incubate and hatch.
If hair strands with viable nits remain on a brush, the eggs are unlikely to hatch at typical room temperatures, which are significantly cooler than the scalp. While nits can remain alive for up to 10 days off the host, they are non-viable because they cannot reattach to a hair shaft or receive the necessary heat. Therefore, nits found on a brush are not capable of starting a new infestation.
Essential Disinfection Steps for Combs and Brushes
Although the chance of re-infestation from brushes is low, cleaning them is a simple and recommended step following an infestation. Disinfection ensures that any remaining adult lice or nits are killed before the items are used again. Effective methods rely on either extreme heat or chemical exposure.
One highly effective method is to soak all combs and brushes in very hot water. The water temperature must be at least 130°F (54.4°C), and the items should remain fully submerged for 5 to 10 minutes to kill both lice and nits. Items that cannot tolerate high heat, such as those with natural bristles or glued parts, should be cleaned using an alternative method.
Other options include soaking the hair tools in a solution of rubbing alcohol or a medicated lice treatment shampoo for at least an hour. Items can also be sealed tightly in a plastic bag and placed in a freezer overnight for at least 12 hours. For the highest certainty of elimination, sealing the items in a bag for two weeks ensures that any lice or nits have died from starvation and temperature change.