Small, isolated and intensively treated
populations are the most likely to become resistant.
In the case of head lice not enough of these studies
have been done to be able to determine the full
extent of resistance to any of the common lice
insecticide. However, there have been instances of
confirmed resistance to permethrin, the
active ingredient in Nix (tm) and other lice control
products but only in certain geographic regions.
Except in some intensively treated
agricultural crops, however, pesticide resistance is
still fairly rare and it has not been found
to be widespread in human lice. Therefore, be
cautious when trying to figure out what went wrong
if a head lice treatment fails because more often
then not the cause is some type of misapplication
or incomplete nit-picking.
The good news is that when resistance is
found the cause is usually intensive overuse
of an active ingredient (pesticide) and this can be
reversed. When use of the active ingredient
is stopped, resistance will diminish and the
population will return to the wild, susceptible
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