Most studies in this group are not comparable because of differences in the formulations used, the concentrations of the active substances and the duration or number of applications. Evidence for activity is limited in each case, and it is possible that some of the effectiveness is partially related to a physical effect, for example sulphur in a heavy greasy base may physically trap and subsequently remove developmental stages of the mite from the skin surface. The mode of action of crotamiton is not understood and there is some doubt about both its acaricidal and antipruritic activities. Similar questions may apply to all of the non-insecticide-based treatments. The fact that these treatments are cheap means that they are more likely to be used in developing countries where source materials may be less well characterised. Most of these compounds have been in use for around 50 years and there is some suspicion that resistance is developing in some areas.16

Figure 37.2 Hyperkeratotic crusts may develop in abnormal sites. With permission from Institute of Dermatology
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