Head lice are a common concern, especially in households with school-aged children. These parasitic insects are highly transmissible. When sanitizing clothing, bedding, and other items that have been in contact with an infested person, the question of effectiveness arises. A household dryer, specifically when using high heat, is a highly effective method for killing both adult lice and their eggs, called nits.
The Science of Heat: Why Temperature is Lethal to Lice
Lice are extremely vulnerable outside the stable, warm conditions of the human scalp. As obligate human parasites, they rely entirely on the host for blood meals and temperature regulation. When removed from the head, adult lice can only survive for about 24 to 48 hours.
Death results from a combination of heat stress and desiccation. Temperatures maintained above 130°F (54.4°C) are lethal to both adult lice and nits. Exposure to this temperature for a minimum of 10 minutes is sufficient to destroy the lice and prevent the nits from hatching. This scientific threshold forms the foundation for using a dryer as a sanitation tool.
Practical Application: Essential Dryer Settings and Duration
To reliably kill lice and nits, the dryer must be set to its highest heat setting, often labeled “high heat” or “cotton/heavy duty.” This ensures the internal temperature reaches the necessary lethal threshold, typically ranging from 135°F to 150°F. Lower or medium settings should be avoided, as they may not generate enough sustained heat to penetrate the fabric.
The duration of the drying cycle is equally important. Items must remain in the high heat environment for a minimum of 30 to 45 minutes. This time frame allows the dryer to fully heat up and for the thermal energy to penetrate the entire load. Items must be completely dry and hot to the touch at the end of the cycle to confirm the lethal temperature was reached.
For items that are washed first, the combination of hot wash water (ideally above 130°F) followed by the high-heat drying cycle provides a double layer of defense. If an item cannot be washed, such as a dry-clean only blanket, place it directly into the dryer on the highest heat setting for the specified duration. For newer, energy-efficient dryers, turn off any automatic or “eco-sensor” settings that might end the cycle prematurely.
Targeting the Life Cycle: Killing Nits and Adult Lice
The greatest challenge in eradicating an infestation is eliminating the nits, or eggs, which are glued securely to the hair shaft. Nits are more difficult to kill than adult lice because they are encased in a tough, protective shell. While adult lice die quickly from heat exposure, nits require prolonged and sustained thermal energy to ensure complete mortality.
The sustained high heat of the dryer denatures the biological components within the nit, preventing it from hatching. If nits are not killed, they will hatch within seven to ten days, causing the infestation cycle to restart.
Therefore, the full 30 to 45-minute duration on the high-heat setting is necessary to successfully target this resilient life stage. Pre-washing items in hot water is often recommended to remove lice from the fabric and ensure uniform exposure to the heat in the dryer. Focusing on the thermal destruction of the nits effectively breaks the reproductive cycle, which is necessary for sanitizing personal items.
Treatment of Non-Dryable Items
Not all items can withstand the high temperatures required for dryer sanitization, including delicate fabrics, toys, and accessories like helmets. For these items, isolation is an effective alternative method. Lice cannot survive for an extended period without a human host for blood meals.
Sealing non-dryable items in an airtight plastic bag is a reliable non-heat approach. This isolation method starves any remaining adult lice and prevents nits from hatching. The bag should remain sealed for a minimum of 10 days, though up to two weeks is often recommended to ensure any newly hatched nymphs perish.
For surfaces that cannot be bagged or laundered, such as upholstered furniture or carpets, thorough vacuuming is the recommended course of action. Vacuuming removes any stray lice or hairs with attached nits that may have fallen off the host. Since lice cannot live long off the head, extensive chemical spraying or fumigation is unnecessary.