Treating head lice according to Sunnah.

The cure for head lice according to the Sunnah of the beloved Messenger of Allah (sallallahu alayhi wasallam) is to shave the hair of the head, where Ka'b bin 'Umra (radhi Allahu anhu) narrated that, "Allah's Apostle (sallallahu alayhi wasallam) stood beside me at Al-Hudaibiya and the lice were falling from my head in great number. He asked me, "Have your lice troubled you?" I replied in the affirmative. He ordered me to get my head shaved. Ka'b added, "This Holy Verse:--'And if any of you is ill, or has ailment in his scalp (2.196), etc. was revealed regarding me. "The Prophet then ordered me either to fast three days, or to feed six poor persons with one Faraq (three Sas) (of dates), or to slaughter a sheep, etc (sacrifice) whatever was available.

Sahih Al Bukhari Volume 3, Book 28, Number 42

The reason for shaving the head is to allow the pores on the surface of the scalp to open and for excess moisture on the scalp to evaporate. This drying process aids the effectiveness of the next step. After shaving the head, one should apply a mixture of cayenne pepper and vinegar to the head, which helps to detach the lice and their eggs from the roots of the hair follicles. After this, they can be washed away. Female children and women need not shave their heads but should apply the mixture of vinegar and cayenne by separating their hair into sections to make the scalp easier to reach.

References -

"And complete the Hajj and 'umrah for Allah . But if you are prevented, then [offer] what can be obtained with ease of sacrificial animals. And do not shave your heads until the sacrificial animal has reached its place of slaughter. And whoever among you is ill or has an ailment of the head [making shaving necessary must offer] a ransom of fasting [three days] or charity or sacrifice. And when you are secure, then whoever performs 'umrah [during the Hajj months] followed by Hajj [offers] what can be obtained with ease of sacrificial animals. And whoever cannot find [or afford such an animal] - then a fast of three days during Hajj and of seven when you have returned [home]. Those are ten complete [days]. This is for those whose family is not in the area of al-Masjid al-Haram. And fear Allah and know that Allah is severe in penalty."

The Qur'an [2:196]