Essential oils are extracted from the plant by various methods and the result is very 
concentrated. Only a few drops are added to and dissolve in the base oil and they are chosen according to their different properties. Many are sedative and relaxing – other stimulating or anti-depressant. Some have an affinity for toning a particular organ such as lungs or liver.
Generally 3 or 4 essential oils are blended together to meet your individual needs. This is the benefit of consulting a professional aromatherapist – I do not use “off the shelf” blends. I also vary the base oils as they contain different vitamins and nutrients.
“the use of specific oils to both detox and invigorate is of great benefit” Tom
Some of the properties of herbs change when the oil is distilled. Do not use essential oils at home without professionial advice as many are harmful during pregnancy or should not be used in certain circumstances.