sorry, one of my biggest bug-bears so will try to explain without getting on my soapbox
all the blardy adverts say that these lotions kill all headlice and you only need to use it once - but generally they only kill live lice so two weeks later you think your kids have got them again but it's just the first lot of eggs hatching.....
it annoys me that people take the easy route because the adds say you just need to use it once, then the little buggers just keep spreading from child to child....
grrrrr