4 doctors weighed in:

How long does it take after nix, (permethrin) to get rid of head lice in a child?

4 doctors weighed in
Dr. Joseph Eastern
Dermatology
2 doctors agree

In brief: Nix (permethrin) is not...

...My favorite treatment, as many strains of head lice are now resistant to it.
Elimite cream (applied to dry hair & left on overnight under shower cap) works better, although not officially approved for that indication. Malathion (ovide lotion) works fastest, but stinks, and is flammable! kwell shampoo also works fast (repeat in 1 week), but like nix, (permethrin) resistance is common.

In brief: Nix (permethrin) is not...

...My favorite treatment, as many strains of head lice are now resistant to it.
Elimite cream (applied to dry hair & left on overnight under shower cap) works better, although not officially approved for that indication. Malathion (ovide lotion) works fastest, but stinks, and is flammable! kwell shampoo also works fast (repeat in 1 week), but like nix, (permethrin) resistance is common.
Thank
Dr. Michael Fisher
Dermatology

In brief: Nix (permethrin)

Permethrin 1% (brand name nix) – this over-the-counter rinse is a synthetic pesticide.
It is the safest of all the pesticide-type lice shampoos. It is not recommended for infants under 2 months of age. The best thing about this shampoo is that it kills both the live lice and the unhatched eggs. It also keeps working for 2 weeks. Therefore, re-treatment usually is not necessary.

In brief: Nix (permethrin)

Permethrin 1% (brand name nix) – this over-the-counter rinse is a synthetic pesticide.
It is the safest of all the pesticide-type lice shampoos. It is not recommended for infants under 2 months of age. The best thing about this shampoo is that it kills both the live lice and the unhatched eggs. It also keeps working for 2 weeks. Therefore, re-treatment usually is not necessary.
Thank
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