Itching is usually worst at the back of the neck or behind the ears. If you look closely, you may be able to see a louse on the crown of the scalp, but it is easier to find them by combing damp hair with a special head lice comb that you can buy from a chemist. Rub a handful of conditioner into the hair first. Earlier this year, New Scientist magazine reported that a professor at Yale University in the USA had invented a shampoo that makes lice eggs glow under ultraviolet light, making them easy to spot. However, it may be some time before his shampoo is in the shops.
Lotions containing malathion, pyrethroid or carbaryl insecticides are effective.
Some lice seem to be resistant, but it is more likely that the lotion has not been applied properly. Leave it as directed on the label, which normally means for at least 12 hours. If you still find nits attached to the hairs, don't worry. They are not normally removed by the treatment, and will eventually grow out or fall off. Repeat the treatment a week later to kill any new lice that have hatched since.