derris dust kills lice very effectively in a few minutes with no survivors to contend with. it is sold in cardboard tubes for shaking over tomato plants threatened by aphids. it's low toxicity to humans and most animals but must be kept away from fish and will kill bees, so is a last resort in gardens. a better cure for both is sound nourishment and a healthy lifestyle, though realistically, if you are hugging lousy-headed people a lot, derris dust is a quick fix. tousle the dust thoroughly through your hair and leave it until you can feel no more lice and can find only dead ones. then brush it out thoroughly and run a fine tooth comb through to remove the dead nits. derris kills nits and all. next time you wash your hair, remember not to let the water you use contaminate waterways where fish may be swimming. it biodegrades rapidly so return it to the soil via your compost heap. i haven't tried pyrethrum, but it's easy to grow and powdered fine with fine talc or similar would no doubt work as well.
i well remember my mother and her slightly older neighbour telling me about the way they cared for the long, lustrous tresses they were so proud of in the 1900s to the 1920s, when they were young women. they rubbed olive oil into the scalp and combed it right through the full length of the hair which was then tightly coiled around curling rags and wrapped in a towel. a plastic shower cap wouldn't 'breathe' as well, but you might need to protect pillow slips with oil-proof cloths.
next day it was washed in water as hot as could be borne with hard castille soap, and rinsed till the water ran clear. in the first rinsing water, an acid helped to remove all traces of soap, but could alter hair colour. lemon juice bleaches, vinegar darkens. canny girls used this property to go or stay blonde or to enrich the highlights of dark hair - lemon juice for blondes, vinegar for brunettes.
the final rinse, to make it soft and shiny and sweet smelling was with rosemary water. boil a small saucepan of rainwater (about four cups) and then throw in a large handful of rosemary to steep until the water is cool. add the liquid to a two gallon bucket of warm rinsing water. using a large jug, pour it through making sure you get through to the scalp. towel dry by patting and not too much rubbing and ideally get some sunshine while it is drying. rain brings out the lustre, too.
i've tried it, but believe me, if your body is badly nourished, and you are producing sick skin exudates, you may have trouble metabolising the oil. as a teenager trying to mature on a diet of fish fingers, white bread and highly toxic tinned sausages, with refined sugar to make it nice, i found my hair was too oily after the treatment, attracted dirt and grit and smelt bad and it took ages to recover. the basis for this beautiful hair was the healthy lifestyle our ancestors lived.
i've found that dry scalp and dry hair are best remedied by health measures designed to improve the way your whole body metabolises fats and oils. cholesterol problems for example disappear when you eat whole grains instead of refined flour. just adding sunflower seeds can help all sorts of skin disorders as well as a range of other health problems.
i've kept angora goats for their fleeces for years, and the beauty of the fleece was directly related not to the 'hoss-gloss' products of the veterinary cosmetics and pharmaceutical industry but the quality of the feed in the paddock.