Lice, Damned Li..., and Regulatory Confusion?
Head lice, Pediculus humanus capitis, are blood-feeding ectoparasitic insects of the Order Phthiraptera found only on the scalps of humans. Since the time when humans started civilised communities, there have always been products based on plant extracts sold for treating head louse infestation. Many of these were derived from traditional herbal practice and the folklore surrounding various aromatic plants, but also included the fixed oil (oils obtained by pressing rather than distillation) derivatives from other plant groups. Some such as olive and coconut oils have been used as grooming aids and hair conditioners for centuries in their countries of origin where they quite clearly have little impact on lice given the levels of endemic pediculosis (Gratz, 1998), but recently some organisations elsewhere have suggested they may have potential for limiting the levels of infestation, although laboratory investigation has shown little or no activity. Other traditional treatments include sassafras oil (from Sassafras spp.) with the active substance safrole (5-(2-propenyl)-1,3-benzodioxole), which is also a carcinogen; and lousebane, Delphinium staphysagria, extracts, which contain the active diterpenoid alkaloid delphinine. So many traditional products are generally either ineffective or potentially hazardous. Following the appearance of multiple forms of insecticide resistance in head lice during the 1990s, the pharmaceutical industry gradually came to the conclusion that products with alternative modes of action were necessary to deal with the increasing level of infestation that was apparent in many communities. In Europe, and more recently Australia, the response to the problem has been primarily directed at development of non-pharmacological methods of treatment, i.e. treatments that are deemed by regulators not to exert a pharmacological effect on the human and which have a physical or chemical mode of action that does not cross the skin barrier. The most basic of these had been a renewed interest in combing to remove lice and their eggs physically but, because a majority of people appear to prefer the simpler approach of a topical treatment, various chemical “active” substances have also been developed that are marketed as having no direct physiological activity. The first products to appear as alternatives to insecticides originated in Central Europe in the late 1980s and mostly claimed to be coconut based; in reality they were mainly surfactant mixes that at some point in their chemical history included a modified coconut derivative. At the time the regulatory status of these preparations was somewhat obscure, being initially sold as “herbal” remedies, and from the mid-1990s they were able to take advantage of the European Community Medical Devices legislation. This process of developing products based on natural substances expanded from using essential oils from the aromatic herbs such as rosemary, thyme, and lavender, and those fixed oils with historical uses in Europe such as olive, grape seed, and coconut oils to include more exotic materials such as oil and extracts from the neem tree, Azadirachta indica, and its close relatives, various other tropical fixed oils, and essential oils from tropical herbs and spices.
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Document Type: Research Article
Publication date: December 1, 2014
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