Are Synergised pyrethrins effective treatment for head lice?

January 18, 2009 | Leave a Comment

What is synergised pyretherin?

Synergised pyretherin is the name given to a chemical insecticide that the Chrysanthemum plant produces naturally.

Are synergised pyrethrins effective for killing head lice?

Head lice have the ability to oxidise the chemicals in synergised pyrethrins quite easily unless a synergising agent is added to boost their pesiticidal effectiveness. The most common additive of this kind is Piperonyl butoxide (derived from petroleum). The FDA states that this chemical combination is both safe and effective (class 1) for use of hair and scalps.

How is this combination used to treat head lice?

The most common carrier for synergised pyrethrins is shampoo that is lathered on wet hair and left for 10 minutes to before rinsing and re-washing the hair with non-medicated shampoo. This treatment will kill live lice but is not completely effective in killing head louse eggs. For this reason, treatment needs to be repeated in 7 – 10 days time to kill off any newly hatched head louse eggs before the nymphs become old enought to breed. This is FDA’s advice even though some products claim to kill both lice and eggs and therefore suggests one treatment for effective head lice elimination.

Cautionary advice about using synergised pyrethrins….

•  If you are allergic to Chrysathemums, kerosene, ragweed or any product derived from petroleum, you must not use synergised pyrethrins to treat head lice.
• In any case avoid using the product near to mucous membranes and wash hands thoroughly after use.
• Some patients are claiming that lice are becoming resistant to synergised pyrethrins. Anecdotal evidence seem to back this up but scientific research is yet to be done on head lice resistance to treatment.
• The Federal Trade Commission website can also be visited to see evidence of patients sold synergised pyrethrins as a product effective in killing head lice in a single treatment who have discovered that this is misrepresentation. This can be distressing for people (already distressed by having head lice) thinking they have effectively dealt with the problem then finding they are still infested with head lice.