The first line treatment for lice is NOT to shave your child's head (as one mother threatened), but to buy one of the over-the-counter products for the treatment of head lice. These products contain either permethrin or pyrethrin.
It is important that a parent follow the directions: using a hair conditioner before the use of the OTC product can diminish the effectiveness, and many products recommend not washing the hair for several days after finishing the application. It is also important to follow the directions for re-applying the product in order to treat hatching lice and lice not killed by the first application. In other words, you must read the package insert!
But with that being said even with parents following the directions to a "T", there are cases where the lice continue to thrive. This may be due to the fact that the lice have become resistant to the OTC products, and different geographic areas do seem to have different rates of resistant head lice.
There are now four fairly new prescription products that have been approved by the FDA for use when OTC products have not worked. These products are Sklice, Natroba, Ovide and Ulesfia. Each of these products contains a different product that has proven to work against the human louse. These prescription products do differ by application time, FDA labeled age guidelines, precautions for use and cost. There is not one product that is currently preferred for use.
Lastly, there has been a study that looked at oral Ivermectin as a therapy for head lice in children over the age of 2. The drug is not FDA labeled for this use. There are guidelines for its use when both OTC and prescription topical agents have failed to eradicate lice.
There is no need to try all of the crazy stuff like mayonnaise on the head, or using Cetaphil on the hair with the blow dryer. There are several areas of the country where there are businesses that will "nit pick" your child's heads, but one of my patients spent $500 dollars on this (for real), but continued to have problems with lice.
So, if the lice won't go, call your doctor before resorting to alternative, unproven therapies.