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Treatment of head lice using physically acting preparations based on silicones is currently replacing insecticide use due to widespread resistance to neurotoxic agents. It has been postulated that some products act by asphyxiation, although the limited experimental evidence and the anatomy of the louse respiratory system suggest this is unlikely.
Observation over several hours of lice treated using 4% high molecular weight dimeticone in a volatile silicone base showed that, although rapidly immobilised initially, the insects still exhibited small movements of extremities and death was delayed. One common effect of treatment is inhibition of the louse's ability to excrete water by transpiration through the spiracles. Inability to excrete water that is ingested as part of the louse blood meal appears to subject the louse gut to osmotic stress resulting in rupture. Scanning electron microscopy coupled with X-ray microanalysis to detect silicon showed dimeticone lotion is deposited in the spiracles and distal region of the tracheae of lice and in some cases blocks the lumen or opening entirely.
Hedrin’s efficacy is a result of its active ingredients, Dimeticone (Hedrin 4% Lotion and Hedrin Once) and Activdiol (Hedrin Treat and Go). All formulations are patented and have been shown to be effective at killing head lice in clinical trials and even work on lice that have developed a resistance to traditional pesticide treatments.
Sample size and Randomisation
Previous studies conducted in the UK have demonstrated efficacy rates for dimeticone 4% lotion of around 70% and no newly emerged nymphs have been found on approximately 50% of participants after first treatment [1,3].