Headlice are small, wingless, parasitic mites that feed upon the blood in your scalp. They can be almost symptomless or itchy in others. They are extremely fast growing, a newly hatched egg will be able to lay eggs after only 10 days; which in turn hatch only a week later. Thus a single lice can become hundreds after a few short weeks.
Most lice can be successfully treated by insectacidal preparations. When they don’t work, it is an application and technique failure rather than a product failure. You should always seek advice from the pharmacist.
Firstly, when treating with the scalp shampoos, they must be at the correct concentration and left in place for the right amount of time. Often a shampoo should be followed by a follow up lotion. Some of the newer non-toxic preparations are very effective against the adults, but are ineffectual against the eggs, so follow up treatments are necessary. The eggs may belying dormant while adults are killed. In all treatments at least a week follow up of treatment is necessary.
Often the headlice are hard to find. A detection process was developed in North Queensland, where almost neat conditioner is applied to the hair. A fine toothed comb is passed through the hair and the conditioner on the comb is wiped upon a tissue. The conditioner is absorbed by the tissue leaving any lice present visible.
The head lice eggs or “nits” are egg cases that are cemented to the hair shaft. The eggs must be physically removed with a fine metal tooth comb. Sometimes a dilute solution of vinegar 1 part vinegar with 4 parts water can be left on the scalp for 3 minutes to soften the eggs. This way the egg casings are easier to remove.
The key point here is that no product will completely kill lice eggs in their “cement bunkers” so repeated treatment is necessary. The egg cases must be removed manually.