They will only live and breed in a very particular micro-climate. No medication, no poisoning just a simple disguise.
Prevention is much easier than cure.
It may not be an overnight instant fix but is is gentle, safe and effective. Rub the oil into the hair , especially the roots and wait a few minutes. Your enemy will now be trapped in the oil, very dozy and be hardly able to move. You will also get out lots of very tiny, so called, nymphs. These will be all sorts of sizes and colours, some so small they are just specks.