Head Lice Questions

Q: My child has head lice and my time is limited. Is it more important to pick nits or treat the house for head lice?

A: Your time is best used removing nits by proper combing with a metal nit comb (see Choosing the Best Lice Comb). Lice die quickly if moved away from the head so cleaning the house or bedding has little positive effect on lice control. Clean bedding, clothes, and household furnishings as the last step in your control program.

Are these "no-nit" policies effective and warranted? No. We do not advocate these policies because they unnecessarily stigmatize students and result in lost school days. We have two main concerns. First, it is very difficult to distinguish live nits from dead nits that remain attached to hair long after lice have hatched (see What are Lice Nits? for an explanation). Therefore it is very difficult to tell when the child is "lice-free". Second, nits can easily be confused with other hair debris so many "false positives" are possible which leads to over treatment. We believe a better approach is to educate parents and teachers about proper lice identification and control so that infestations can be effectively managed when they occur (see Safely Eliminating Head Lice).

Q: Do head lice carry any diseases that can be spread when they bite?

A: Head lice are not important vectors of human disease. The best evidence of this is the fact that while head lice infestations are common and widespread no human disease outbreaks have been associated with these infestations. However, scratching of itchy bites can cause secondary bacterial infections.

Q: Are head lice resistant to the medications (insecticides) in lice shampoos and creme rinses?

A: Lice shampoos and creme rinses contain either pyrethrin or permethrin as the active ingredient. Insecticide resistance (see What is Insecticide Resistance?) to permethrin and pyrethrin has been detected in some populations of head lice but the extent of the resistance is not well known. What we do know is that resistance to any pesticide tends to be patchy, high in some areas and low or non-existent in other areas. Patterns of resistance tend to follow patterns of overuse of the pesticide. And, the frequency of resistance can decline when the use of the pesticide is reduced.

Therefore, even with some reports of insecticide resistance in head lice, it is likely that in most treatment failures probably have another cause. I believe that resistance is spotty and of relatively low intensity in most head lice populations. Under these conditions pyrethrin and permethrin-based treatments are still the best approach when combined with thorough nit removal by combing.