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Medications for Head Lice

Is Head Lice Medicine Always Effective?

Like germs that are resistant to antibiotics, some lice also develop resistance to the medicine used to kill them. Resistance tends to be scattered, however. It may be present in one neighborhood, but not another.
Medications may seem not to work for many reasons. This may include:
  • Misdiagnosis
  • Not following the instructions
  • Resistance
  • The nits survive
  • Reinfestation.
Misdiagnosis of a Head Lice Infestation
A diagnosis of head lice can be made if a person has adult head lice on the head or many lice eggs within a ¼ inch of the scalp (about the width of your little finger). Nits found on the hair shaft further than a ¼ inch from the scalp have already hatched. Head lice treatment is not recommended for people who only have nits further than a ¼ inch away from the scalp.
Not Following the Instructions
Problems can occur when applying the medication. Common ones include:
  • Making the hair too wet with water before applying a pediculicide (an agent used to destroy lice), which dilutes it.
  • Using a cream rinse or conditioner shampoo before applying a pediculicide, which interferes with the medication.
  • Failure to leave the pediculicide on long enough. Carefully follow the instructions that come with the product.
  • Reshampooing the hair immediately after applying the pediculicide. Wait one to two days after treatment before washing hair again (except with benzyl alcohol lotion and spinosad, in which case the hair may be washed immediately after use).
  • Inadequate amount of medication. Extra-long hair may require multiple bottles of pediculicide to fully wet it.
  • Not combing. Using the medication alone may not be enough to cure a head lice infestation. Combing the hair to remove lice and eggs has been shown to help.
Resistance to Head Lice Medication
If the medication does not kill any crawling bugs within 24 hours, then resistance is likely. If the medication kills some of the bugs, or if the bugs are twitching 24 hours after treatment, then resistance to medication is probably not occurring.
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