How long does a louse live outside a human body? - briefly
A louse can survive away from a host for roughly 24–48 hours; under optimal temperature and humidity it may persist up to about 72 hours before dying from dehydration.
How long does a louse live outside a human body? - in detail
Lice depend on blood meals; without a host they die rapidly. Survival time varies among species and environmental conditions.
- Head lice (Pediculus humanus capitis) survive up to 24 hours on a dry surface. In high humidity (≥80 %) and temperatures around 20‑30 °C, they may persist for 48 hours, but they lose the ability to feed after 1‑2 days.
- Body lice (Pediculus humanus humanus) live longer on clothing or linens. Under optimal humidity and moderate temperature, they can remain viable for 5‑7 days. They hatch from eggs on fabric, but the adult stage requires a host within this window.
- Pubic lice (Pthirus pubis) behave similarly to head lice, surviving no more than 48 hours off a person, with reduced longevity in dry or cool environments.
Key factors influencing survival:
- Humidity: Low moisture accelerates desiccation; high humidity prolongs life.
- Temperature: Extreme heat (>40 °C) kills within minutes; cold (<5 °C) can incapacitate within hours.
- Substrate: Soft fabrics retain moisture, extending viability; hard surfaces dry out insects quickly.
- Stage: Nymphs and adults are equally vulnerable; eggs (nits) cannot hatch without a host’s body heat and remain inert.
Practical implications:
- Launder clothing and bedding at ≥60 °C or use a dryer on high heat for at least 30 minutes to ensure eradication.
- Dry cleaning or sealing items in a sealed bag for 2 weeks eliminates surviving insects.
- Vacuuming and thorough cleaning of furniture reduce the chance of re‑infestation.
In summary, lice survive only a few days without a human source, with body lice persisting slightly longer on garments, while head and pubic lice rarely exceed two days under typical indoor conditions.