Lice can pair within the first 10 hours of their adult life, and pairing occurs frequently. Female head lice lay an average 3 or 4 eggs (nits) a day, but some may lay considerably more. Nits are usually laid near the junction of the scalp and the hair shaft. About 70% of egg laying is single eggs on single strands of hair, but multiple numbers are sometimes laid on a single hair. They are attached with a very strong glue and cannot be easily removed with today's head lice products.
The eggs hatch within 7 to 11 days. Since other shampoos do not kill all of the eggs or dissolve the glue holding the nits to the hair shaft, they must be repeated one week later to kill the newly hatched larvae. Once hatched, developed lice take 8 days to become adults and the cycle begins all over again.

Why other shampoos are ineffective on nits

1. None of the current shampoos kill ALL the eggs. In Israel, over 40 different pyrethrin formulations were tested in a laboratory. The greatest mortality achieved was 80% for adults and nymphs and 30% for eggs. Common Sense Quarterly Report (B.I.R.C.) Fall 1998 Because these products seem to have little ovicidal (egg killing) activity, a second treatment is often necessary to target lice that hatch after the initial treatment. Department of Immunology and Infectious Diseases, Harvard School of Public Health
2. Other shampoos do not dissolve the glue cementing the nits to the hair shaft. The nits remain on the hair and the live ones hatch in 7-11 days.

NO NIT POLICY - Many schools have established a "no nit" policy, meaning that children are denied readmission to the classroom until their heads are free of nits. Thus, it is important to address the nits as well as the head lice.

If none of the other shampoos in a single application kills all of the nits and dissolves the glue, which holds them to the hair shaft, you can generally expect more head lice in 7 to 11 days. This will require a second application to complete the treatment.

This necessity has become so much of a problem that the Federal Trade Commission (FTC) recently cited the manufacturers of three head lice products (Rid, Clear, Pronto) stating that they should make it clear that their products are not 100% effective in a single application. They were instructed to state in their advertising, "Reapplication and egg removal are required to ensure complete effectiveness." Associated Press 9/19/98

Lice B Gone has not been proven to kill the nits, although numerous reports indicate that after one application, they are not viable. It does, however, soften the glue that holds the nits to the hair shaft, allowing for easy removal with a nit comb. Be sure to allow the product to remain on the hair for the recommended thirty minutes.

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