Vinegar has been used for thousands of years; in fact, the earliest traces of the fermented liquid were found in Egyptian urns from around the year 3000 BC. Vinegar is the end product of fermentation, which is the breakdown of sugars by yeast and bacteria. First you get alcohol, then, as it breaks down further, you get vinegar.
Vinegar can be made by the fermentation of various fruits and grains, or from beer or wine. It is commonly used for culinary purposes, often as an ingredient in salad dressings, sauces, condiments such as mustard and ketchup, and marinades.
For head lice, plain white vinegar works just fine. Apply undiluted vinegar to the hair, paying particular attention to the scalp, as well as the areas around the neck and behind the ears. After a few minutes, rinse with a solution of half vinegar and half water; then comb the nits (baby lice) out of the hair with a lice comb. Repeat daily for a couple more days, or until you see no more eggs or live nits.
Why it Works
The acid in the vinegar works by dissolving the exoskeleton of the live nits, and the protective shell of eggs. This kills the eggs, and makes the nits less "sticky" in the hair, making them easier to comb out. In this way, vinegar disrupts the life cycle of the lice, and should result in complete eradication within a week.
Vinegar does NOT work on adult lice, only on nits and eggs. Do not apply vinegar to a scalp that is red and irritated (which can happen after a prolonged infestation) because it will cause severe pain. Take care to keep vinegar out of the eyes.