How long is a person contagious for head lice?

As long as lice or nits are still found on a person or their clothing, they can spread it to others. Lice have an approximate lifespan of 24-25 days. Adult lice each lay up to 150 nits or eggs about a week after they have hatched out. The nits hatch within 7 to 10 days. After hatching they take 8 to 9 days to become adults at which time the female louse starts laying more eggs and the cycle repeats itself. Although lice cannot live without a host, the nits do seem to survive off the head.

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