Aromatherapy has been believed to be only the act of smelling an aroma, a scent, but it is more than that. It refers to the use of essential oils in a therapeutic way.
You may have noticed that some oils are more ‘oily’ than others. The reason is their chemical (and therapeutical) properties. On one hand, we have the expressed (fatty) oils, which are derived from plants and animals and do not evaporate. Examples of these oils are all cooking oils you see at the store. On the other hand, we have volatile (essential) oils which evaporate easily. They come from aromatic plants and do not contain any vitamins nor minerals as the expressed oils do.
The healing powers of essential oils come from hundreds of aromatic molecules contained in each bottle. These molecules have pharmacological and physiological properties that have a particular effect on the human body regardless of the organ and/or its function to keep the person healthy and in balance.
What you obtain in a small bottle of essential oil is the result of a great number of certain parts of a plant and the extraction process needed for a particular oil and its source.
One thing to keep in mind is that essential oils do expire. What happens is that the more exposed is the oil to the air the sooner it will lose its properties. So, to be on the safe side, your essential oil is good for up to two years.