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Frequently Asked Questions
Q: What's the difference between pyrethrins and permethrin?
A: Pyrethrins are naturally occurring compounds extracted from chrysanthemum plants. Insects possess mechanisms to break down pyrethrins so a synergist, piperonyl butoxide, is usually added to the formula. The synergist inhibits insects' ability to break down the pyrethrins. Permethrin has the same basic chemical make-up but is synthetically enhanced to be more effective. Permethrin has much longer residual activity and does not require a synergist.
Q: Can my dog or cat transmit lice to my children?
A: No. Head lice are specific to humans. If a head louse is removed from its human host, it will die within a day or two.
Q: How big are lice?
A: An adult head louse is approximately 2.5 mm to 3.5 mm long. A louse egg, or "nit," is about 0.5 mm to 1 mm long.
Q: I've heard that head lice are resistant to some lice treatment. Is this true?
A: In some places, potential resistance to several different lice-killing agents has been reported. Experts are trying to determine to what existent resistance exists. The best way to avoid a resistance situation is to follow the directions on the product label closely. Improper application of lice-killing chemicals has contributed significantly to the presence of resistance in lice.
Q: How long do lice live?
A: A louse egg hatches about 10 days after it is glued to a hair shaft. Upon hatching, a louse molts three times over a 10- to 12-day period before its final molt into a mature adult. Adult lice can live up to 40 days.
Q: How long after my child contracts lice will I be able to detect them?
A: A single female louse can lay several eggs each day. Within a couple weeks, a child may have dozens of immature lice. The more lice present, the more quickly the child will feel an itchy scalp, which usually leads to an inspection by a parent or school official. Looking for one louse or one nit might be difficult, but dozens should be readily apparent through close inspection.
For more information about head lice, please visit the University of Florida's School IPM Web site (http://schoolipm.ifas.ufl.edu). Click on Technical Information - Pests, then select "Biology and Control of Head Lice."
Edited by: Angela Brammer, University of Florida
