History

At the time medieval, the various odors of grasses were determining as for the use which people made. Thus, when a plant was recognized to move away the insects they supposed that it was to be good to move away the insects inside the house. 
At that time, people suspected that the insects could transport diseases, often very serious. Or certain grasses were used to purify the ambient air which one believed able to transmit certain diseases. 
The paths, on which the royal processions of the last centuries rolled, were strewn most of the time with grasses dried like rosemary, thyme or the street. They had as an aim to protect the sovereigns and their families from diseases, like the plague. 
It is with the Average East as in Far East that essential oils were initially used. Ayurveda medicine originating in India in fact a significant use.  
It is in Arabia which the techniques of distillation began and which they were also sophisticated.  
It seems that the methods of extraction per vapor are still the best proceeded to preserve the perfumes of the aromatic plants and their therapeutic capacities.  
It seems that they are people who took part in the crusades which brought back these techniques in occident, here now several centuries.