**Abstract**

Essential oils are complex mixtures of terpenes and phenylpropanoid compounds, present in multiple species of aromatic plants. They are extensively used in food and cosmetic industries in order to give flavor to food and drinks or as natural fragrances. Moreover, several compounds present in essential oils are important for the pharmaceutical industry due to their antioxidant, antimicrobial, anxiolytic or spasmolytic effects. Although many essential oils are generally recognized as safe, a series of adverse reactions have been reported after their use either by internal or external routes. The aim of this chapter is to increase the awareness of healthcare professionals concerning possible safety issues of essential oils. Common adverse effects of essential oils like sensitization and dermatitis but also more severe phenomena like neurotoxicity will be presented in detail, concerning their epidemiology, mechanism and clinical significance. A thorough understanding of the safety profile of essential oils is necessary for healthcare and food industry professionals in order to maximize their beneficial effects while minimizing the risk for the users.

**Keywords:** essential oils, terpenes, sensitization, neurological toxicity, endocrine disrupting potential
