A study amongst Welsh school children, published in the journal Archives of Disease in Childhood, has found that four out of five headlice are now resistant to treatments, such as permethrin and the organophosate malathion, which are traditionally used to eradicate them. The researchers combed their way through the heads of 300,000 school children from 31 schools. They then tested samples of the lice they collected to measure their resistance to treatment, including the levels of enzymes such as glutathione transferases, mono-oxygenases and esterases. Of 316 lice tested, 80% were resistant to the standard treatments. Healthcare workers in Wales are now presumably scratching their heads as they try to decide what to do about the problem. Although the study was conducted in Wales, the same treatments are used almost universally for headlice, so it's likely that what's true for Wales is going to be true elsewhere too. Thankfully help might be at hand in the form of newer silicone-based lotions, to which the lice are reliably sensitive.