ABSTRACT
INTRODUCTION Essential oils are incorporated into many products designed for cosmetic and dermatological uses. Their use is based on claimed efficacy against a wide variety of ailments and their potential as fragrances. Their safety, particularly at the low levels present in formulated products, is most frequently not questioned because of their long history of reasonably safe use and a low incidence of serious adverse side effects. However, in some instances, the level of evidence required from regulatory agencies to confirm safety has risen. In contrast, as long as claims are limited to cosmetic nontherapeutic indications, the thresholds for efficacy evidence set by regulatory agencies remain relatively low. Increasingly though, a more substantial and higher quality evidence of efficacy is becoming available for many essential oils. This chapter follows from Chapter 24 and emphasizes the provenance, use, and potential toxicity of tea tree, peppermint, eucalyptus, lavender, and chamomile essential oils. Where available, in vivo data with a relevant route of exposure based on complete oils have been used as such data give a functional assay with direct relevance for hazard and risk evaluations. When data on individual constituents are used or when data originate from in vitro studies, a critical assessment is needed. Thus, data from individual constituents ignore the potential for interaction (agonistic or antagonistic effects) and in vitro assay ignores the possibility that not all constituents may reach the target for toxicity due to differences in absorption, metabolism, or elimination.
