Head lice live in hair, typically laying eggs (called nits) at the base of the hair shaft. Treating lice can be a long and miserable process, especially due to the difficulty in finding every egg and every louse. Nits can be harder to locate, and are probably the worst part of getting rid of lice. But there are ways of determining whether a nit is dead or alive, which may help in the lice-removal process.
Determine whether the nit you are looking at is actually a louse egg. What you may be seeing is a bit of hairspray or dandruff, or some other sort of debris. So grab a magnifying glass and make sure that the debris is oval-shaped, and whether it can easily be swiped away. Lice eggs are glued to the shaft of the hair, and will be harder to pull from the hair strand.
Understand that where the nit is located may help you to make a better judgment as to whether the nit is dead or living. If you locate a nit close to the scalp, it is probably still alive. This is because female lice lay their eggs near the root of the hair. If the nit has moved further down the strand of hair, it follows logic that the nit may have already hatched, as it took time for the hair to grow to have the nit situated so far down the hair. According to the Centers for Disease Control, if the nit has travelled a quarter inch down the length of the hair strand, it probably has either hatched or died.
Try to pull the egg out of the hair, and see whether it is easier than usual to remove. If so, this most likely means that the egg no longer houses a live embryo.
Determine the colour of the nit. If it is white in colour, this probably means the nit has died. If the egg is darker in colour, it usually means that the nit is still active.
Because most schools have "no nit" policies that keep children from coming to school if they have any (dead or alive) eggs in their hair, it is to your benefit to try and remove any nits you find if you have a child in school.