You scratch your head, but no earth-rattling thoughts are forthcoming. Last week the neighbor's kid tried on your Mountain Equipment Co-op hat, and now your girlfriend's head itches, too. Ohmigod. Head lice. If the social stigma doesn't do you in, imagine how nasty it will get if the bites become infected.

Chemical firms insist you need their toxins to stop scratching, but it isn't true.

Left untreated, these bloodsucking insects can multiply, and their bites may enlarge your lymph nodes and induce fever and severe weight loss. And just as bad, your pharmacist or doctor will likely steer you in a direction you don't want to go: chemical treatments. If you don't want the stuff on your lawn, why would you put it on your head?

The toxic shampoos prescribed to kill lice are poison to the human nervous system, and there's new, though controversial, evidence that they can throw your hormones out of whack as well. Their most common ingredient, pyrethroids, don't even work very well because lice, just like bacteria fed a steady diet of antibiotics, have developed resistance to it.

The scary thing is that consumers might use more and more of it to get poorer and poorer results. Pyrethroids are also dangerous for people with allergies to chrysanthemums, ragweed and kerosene and other petroleum derivatives.

Other readily available anti-lice potions contain acetone, the same smelly agent that takes nail polish off, or lindane, a highly toxic and persistent chemical that a number of anecdotal reports have linked with seizures and death in exposed children. And to double the dilemma, when you rinse your hair, lindane in particular moves into the water supply and the food chain.

Does mother nature provide any answers? Health food stores and some drug marts sell shampoos containing essential oils like tea tree, eucalyptus and oregano, and while one would think they wouldn't be as bad as laboratory brews, the long-term effects of intensive use haven't been studied. Even holistic-minded delousers say tea tree compounds have some similar properties to synthetic chemicals, and over time lice could develop resistance to "natural" insecticides as well.

What to do? Cutting-edge prevention and treatment is low-tech and labor-intensive. The key is faithful and proper use of tweezers, a magnifying visor and the crucial high-quality anti-lice comb.

We're talking deluxe stainless steel (thus boilable) models that efficiently remove the noxious insects and their silvery white eggs (nits) from your hair and clear up an infestation in a couple of days.

Combs are sold at drugstores, but the best are available at the non-profit http://www.headlice.org/. What the experts say "I don't agree that pyrethroids have low mammalian toxicity. It's dose-related. Pyrethroids are based on a natural substance but are chemically altered to persist (in the ecosystem). They are neurotoxins. Lindane can affect the kidneys, liver and pancreas as well as the endocrine system. My daughter's school had lice. We used no chemicals -- it's not a big deal when you know what you're doing. We used tea tree oil and combing. Do it like clockwork and the lice just disappear." JULIA LANGER, World Wildlife Fund, former director of toxicology programs

"Permethrins (synthetic pyrethroids) have an excellent safety profile that has been extensively confirmed in clinical trials. There are studies of lice developing resistance, but they all report localized resistance -- as in one area of the city. The (U.S.) Center for Disease Control says there is no satisfactory method of getting rid of an infestation apart from chemical treatments.'' JANET WATSON, GlaxoSmithKline Inc., makers of R&C shampoo and Kwellada-P creme rinse

"We can't exonerate head lice from the transmission of disease. Still, there are many reports of deaths from pesticides (lindane). We can't remove every chemical exposure from a child's life, so we have to be careful about the ones we can control. The most effective treatment is the traditional grandmother way -- screen vigilantly and remove manually." DEBORAH ALTSCHULER, National Pediculosis Association.

JOHN CLARK, PhD, director, Massachusetts Pesticide Analysis Lab "People are under the illusion that just using a pesticide is going to solve the problem, but you have to remove all nits and lice. You need a special comb, pillow case and sheet washing, and vacuuming of carpets."