Pesticides don’t work any more for head lice. Head lice have developed resistance to pesticide shampoos. Nothing kills lice eggs. So the lice eggs (known as Nits ) continue to hatch once you have washed out the lice shampoo. What you are left with is the need for mechanical removal of the lice eggs, or nits. If you don’t get every single lice egg out of the hair, the head lice colony will start right up again.