**11. Photo toxicity of essential oils**

The essential oils of some aromatic plants contain some photoactive compounds in their composition. Psoralens present in essential oil of citru bergamia were found to effective for binding of mono and biadducts produced under UV-light. These were found to mutagenic and cytotoxic [112]. However, in the dark, this oil is not cytotoxic or mutagenic by itself. It has been noted that *Fusanus spicatus* wood essential oil was not phototoxic but was very cytotoxic. In other words, cytotoxicity seems rather antagonistic to phototoxicity. In the case of cytotoxicity, essential oils damage the cellular and organelle membranes and can act as pro-oxidants on proteins and DNA with production of reactive oxygen species (ROS), and light exposures do not add much to the overall reaction. In the case of phototoxicity, essential oils penetrate the cell without damaging the membranes or proteins and DNA. Radical reactions by excitation of certain molecules and energy transfer with production of oxygen singlet occur when cells are exposed to activating light. This may cause damage to cellular macromolecules and in some cases the formation of covalent adducts to DNA, proteins and membrane lipids. Obviously, cytotoxicity or phototoxicity depends on the type of molecules present in the essential oils and their compartmentation in the cell, producing different types of radicals with or without light exposure. However, such an antagonism is not quite a strict rule [86]. It was also found that *Citrus aurantium* dulcis (*Citrus gracilis* subf. dulcis) and *Cymbopogon citratus* essential oils were phototoxic and cytotoxic. Therefore, the potential toxicity of essential oil should be considered before use as antibacterial for human as well as for animals [113].
