Lice eggs, also known as nits, are one obvious signal of a lice infestation. These eggs stay tightly attached to individual hair strands even after the lice have hatched out of the eggs. Unlike live eggs, dead lice eggs can be present even when you have successfully killed the lice infestation. If you do not pay very close attention to the leftover egg shells, it can be difficult to tell whether the egg is alive, empty or completely dead. With a little extra attention, however, you can learn to tell the difference between the three types of lice eggs.
Look very closely at a nit and observe its shape. A live nit will be plump and have a small, but visible bump on top. A hatched egg will be plump and rounded like a live egg, but the top will be flat and will not have a bump. Dead nits have a distinctly different shape -- they still have the bump on top, but the rest of the egg should be crumpled inward.
Observe the egg's colour. This can help you differentiate between hatched and dead eggs, as hatched eggs will be pale or white while dead eggs will be brown. Unfortunately, live eggs are also brown, so do not use colour as your only indication of whether an egg is dead.
Pluck the egg in question off the hair and smash it between your fingernails. If you can feel or see it pop, the egg was still alive. If it did not pop, however, it was dead. From this information, you can conclude that a brown egg that did not pop between your fingernails was dead before you tried to smash it.
The egg's distance out from the scalp on the strand of hair can provide an indication of whether it is alive. Lice may lay eggs up to 1/2 inch from the head -- if the egg is significantly further out on the hair than that, it is probably old and dead.