Essentials oil are defined as complex natural substances. Their composition varies according to the geographical origin of the plant, the part of the plant used, the conditions of production or the method of production. The number of components present in these volatile oils can be very high, despite a structural variation rather limited (3 major atoms: carbon, hydrogen and oxygen). All these characteristics justify the difficulty of carrying out a reliable and relevant toxicological assessment of these ingredients, which are very popular in cosmetic industry. Thanks to chromatographic methods, it is now possible to know the nature and concentration of all the compounds present in an essential oils mixture. Thus, trhough analysis reports obtained by chromatography, the maximum acceptable concentration of a mixture for a given finished cosmetic product can be determined on the basis of the compound identified as limiting. The toxicological approach here applied is mainly based on the QRA methodology (Qualitative Risk Assessment) used for the calculation of IFRA certificates. Each compound identified by chromatography has a toxicity reference value (TRV) and a theoretical skin absorption rate. In the absence of TRV, the Threshold of Toxicological Concern approach (TTC - Cramer) will be applied.