Evidence indicates that the most widely used treatments for head lice (pesticide based shampoos) may be losing their effectiveness. USA Today 4/29/97
THE HARVARD STUDY - Published studies from the Czech Republic and Israel and findings from Harvard University support the theory that there are new strains of "super lice" that can survive pyrethrin and permethrin, the pesticides used in head lice shampoos. In the Harvard Study, lice collected from Cambridge, Mass., Boise, Idaho and the Philippines were placed on permethrin-soaked paper. The lice gathered from the Philippines (where such shampoos are not used) all died quickly. By contrast, the lice gathered from the US did not. Wall Street Journal 8/12/98
PYRETHRINS / PERMETHRINS - Natural pyrethrins were introduced into the US in the 1980s as a less-toxic alternative to lice shampoos containing lindane (Kwell, etc.). A number of pyrethrin formulations are sold over the counter, such as Rid, Clear, A-200 as well as many private label brands with the same formula. Lice that are resistant to pyrethrins are also resistant to permethrin products like Nix and pyrethroids (synthetic pesticides having a chemical formula similar to natural pyrethrins). As a consequence, the entire pharmacological class is becoming less valuable. Common Sense Pest Control Quarterly (B.I.R.C.) Fall 1998
The marketing of permethrin in Israel started in 1991. The first reports of resistance were in 1993, a time equivalent to 40 generations of lice. Similarly, resistance was reported within four years of introduction in the countries of France, the Czech Republic and Great Britain.
PHYSICIANS - Because of resistance and product failure, some physicians have overreacted by prescribing repeated use of products, stronger formulas or longer application times. These practices should be discouraged!
History indicates that lice eventually grow resistant to every effective
insecticidal treatment used against them. When will we learn?
A BRIEF HISTORY OF LICE DEVELOPING RESISTANCE TO PESTICIDES
DDT - The age of synthetic pesticides for lice treatment started with the synthesis of DDT in 1939. During World War II, DDT was used with great success when the population of Naples was dusted with it to stop the typhus epidemic. At that time, DDT effectively killed body lice. Less than 10 years later, during the Korean War, body lice could not be stopped with DDT due to the resistance they had developed. Head lice resistance to DDT was later seen in Britain in 1971. Today, head lice throughout the world remain resistant to this harmful pesticide.
LINDANE (Kwell) - Lindane is an organochlorine pesticide that has been used for lice treatment for about 50 years. It was used for chemical warfare in World War I but by luck (if you want to call it that), its efficiency for lice was discovered when soldiers were found to be lice-free after exposure. During the Korean War, when lice became resistant to DDT, the substitution of lindane, for a period of time, controlled them successfully.
Head lice resistance to lindane has been reported in many parts of the world, including Israel, Canada, Denmark, Malaysia and the US. Lice in the Netherlands had grown so resistant to lindane in 1978 that two treatments gave only a 65% cure rate. When it was introduced in the 1950's, one treatment given of the same formulation was 100% effective.
MALATHION / CARBARYL - When head lice in Britain became resistant to DDT and lindane in 1971, malathion and carbaryl were tested. The first reports of lice resistance came from agricultural areas. Chronic malathion exposure of the agricultural workers there may have contributed to the resistance that head lice eventually developed. As late as 1995, resistance to malathion was still being reported in Britain. Unfortunately, some doctors still prescribe the malathion containing product called Ovide for head lice.
CONCLUSION - As you can see throughout history, when one pesticide fails to remain effective, another is chosen and put into use. Without ever knowing their potential long-term health consequences, we simply substitute one pesticide for another and hope that the head lice do not develop a resistance. This never happens. Head lice have demonstrated time and time again that nature's "adapt and survive" programming will eventually help them to develop a resistance to that pesticide as well.
LICE B GONE - One of the challenges to successfully treating someone with head lice is that you have two distinctly different problems you are trying to solve simultaneously; kill the head lice and kill/remove the nits. Before Lice B Gone was developed, attempting to kill the head lice with pesticides was the logical first step. After many applications, numerous generations of lice were exposed to the chemical causing "super lice" to evolve that could withstand future doses of the pesticides. The nits, however, were a more complex problem when the pesticides did not kill all of them. The ones that lived remained glued to the hair and hatched in 7-10 days. Then you had to start all over again. This is why the labels on the other products state that you have to use them twice today and again 7 days later when the nits hatch twice the harmful pesticides, twice the application time and twice the overall cost.
With Lice B Gone, one application gets rid of head lice and the nits because it softens the glue that holds the nits to the hair shaft, allowing them to be easily combed and rinsed away. Thus, the "resistance factor" never becomes an issue. The head lice and nits are off the head and down the drain in 30 minutes, eliminating the possibly of any type of resistance developing.