How long does it take for Permethrin to kill a louse?

Factual Questions
1

The instructions on the bottle say to leave the kid’s hair soaked in the chemical for ten minutes. I am curious to know whether this means it takes 10 minutes to kill a louse with permethrin, or if the ten minutes is just to make sure all the lice get fully mired in the stuff.

I ask because I have a louse in a baggy, and I have doused it with permethrin, and it seemed to survive–but possibly I simply didn’t douse it for long enough. Should it die quickly on immersion, or do I need to do this again for a full 10 minutes?

I am doing this to figure out whether my kid has permethrin-resistant lice, which is apparently a thing.

2

So did it die?

3

Permethrin is a residual insecticide. By soaking the hair for 10 minutes you give the chemical time to bond to the hair. Once it is bonded to the hair any insect that crawls over it will absorb the pesticide and die. The idea being that rather than just killing the lice that are there, the insecticide also kills any new lice that may be picked up or any larvae that hatch from eggs.

If you just want to kill the lice that are present, you don’t need to soak the hair. Of course you don’t need to use insecticidal shampoo at all. Plain old detergent will kill the adults.

Permethrin by itself doesn’t kill particularly fast acting. It should incapacitate within a few minutes, but death comes from dehydration and exhaustion, which can literally take days.

I’m curious by what you mean by “doused it with permethrin” All the insecticidal shampoos I am familiar with are either surfactant or oil based, and the surfactant or oil all by itself will kill within minutes, so whatever the problem is, it’s not likely to be insecticide resistance.

4

I had the thing in a ziploc bag with some permethrin-based “creme rinse”. (Off brand, ingredients identical to “Rid” brand.) The insect was completely submerged within the glob of creme rinse for twenty minutes. After twenty minutes I pulled it out and got all the creme rinse I could off of the thing, and then placed it inside a new empty ziploc bag. For a long while, it appeared dead, but about an hour later I could see it was moving its limbs, and it is now walking around inside the bag, though much more slowly than before. (This appears to be consistent with what you said about it incapacitating them but not killing them at first.)

What is it about the surfactants or oils which should have been sufficient to kill it?

5

It is either still alive or zombified.

6

And now we have patient zero for the zombie apocalypse.

Nice job wiping out humanity Frylock :mad:

7

It was dead the next morning fwiw.