Head lice is a big, big concern for parents of young school age children. From Science Daily:
Eggs from head lice, also called nits, are incredibly difficult to remove. Female lice lay eggs directly onto strands of hair, and they cement them in place with a glue-like substance, making them hard to get rid of. In fact, the eggs are glued down so strongly that they will stay in place even after hair has been treated with pediculicides -- substances used to kill lice.
Some shampoos and conditioners that contain chemicals or special oils are marketed as nit-removal products. However, new research just published in the Journal of Medical Entomology shows that ordinary hair conditioner is just as effective.
In an article called "Efficacy of Products to Remove Eggs of Pediculus humanus capitis (Phthiraptera: Pediculidae) From the Human Hair," scientists from Belgium gathered 605 hairs from six different children. Each hair had a single nit attached to it. Approximately 14% of the eggshells contained a dead egg, whereas the rest were empty.
They then tried to remove the eggs and tested the amount of force needed to do so. They found that nits on the hairs that were left completely untreated were the most difficult to remove. Eggs on hairs that had been soaked in deionized water were much easier to remove, as were the eggs on hairs that had been treated with ordinary hair conditioner and with products specifically marketed for the purpose of nit removal.
However, they found no significant differences between the ordinary conditioners and the special nit-removal products. In all cases, less force was required to remove the nits after the hair had been treated, but the effectiveness of the products was essentially the same.
The authors hypothesize that the deionized water was effective because it acts as a lubricant, so less friction is needed to remove the nits from the hairs. The same goes for the conditioners.