The in vitro cytotoxic activity on human cancer cell lines of sixteen commercial EOs such as Aloysia triphylla , Boswellia carterii , Boswellia serrata , Cinnamomum zeylanicum , Cistus ladanifer , Citrus × aurantium , Citrus limon , Citrus sinensis , Cymbopogon citratus , Foeniculum vulgare ,