How long do lice live without a host? - briefly
Adult head lice survive roughly 24–48 hours without a human host, and nymphs endure a comparable period. In optimal, humid conditions they may persist up to five days, but they quickly die from dehydration.
How long do lice live without a host? - in detail
Lice are obligate ectoparasites; they require a living host for feeding and reproduction. Outside a host, their survival depends on species, temperature, humidity, and stage of development.
Adult head lice (Pediculus humanus capitis) can endure up to 48 hours in optimal conditions—moderate temperature (20‑30 °C) and relative humidity above 70 %. In cooler, drier environments, mortality occurs within 12‑24 hours. Body lice (Pediculus humanus humanus) exhibit similar limits, though they may persist slightly longer (up to 72 hours) because they are adapted to clothing habitats that retain moisture.
Nymphs are more vulnerable. Without access to blood, they survive no more than 24 hours under favorable humidity; lower humidity reduces survival to 6‑12 hours. Eggs (nits) are inert; they remain viable for several days but will not hatch without a host’s warmth and carbon dioxide.
Key factors influencing off‑host longevity:
- Temperature: 20‑30 °C maximizes survival; temperatures below 10 °C or above 35 °C accelerate death.
- Relative humidity: Levels above 70 % prevent desiccation; humidity below 40 % leads to rapid dehydration.
- Stage: Adults outlast nymphs; eggs remain dormant but require host conditions to develop.
- Species: Head lice die faster than body lice when removed from a host because body lice are accustomed to surviving on clothing for longer periods.
Practical implication: removing infested clothing, washing at 60 °C, and drying on high heat eliminates lice within the window of their off‑host survival. Immediate isolation of personal items reduces the risk of re‑infestation, as the parasites cannot survive beyond the maximum periods outlined above.