Essential oils are the odorant chemicals extracted from plants. Aromatic plants grow in great numbers but not all of them yield enough essential oil to make it worthwhile to go through the extraction process. Some of them also have a very toxic effect and therefore cannot be used for therapeutic purposes in the practice of aromatherapy.
When one asks what is an essential oil, it is useful to think about their characteristics and appearance. Essential oils are fluidic, odorant, colored and volatile. This means they undergo chemical changes when they come into contact with sunlight, air and heat. They are not water-soluble but will dissolve in pure alcohol or chemical solvents such as fatty or oily substances, petroleum and ethers.
Essential oils have a density generally lighter than water which causes them to float on the surface of water. There are however some essential oils that are heavier and will sink to the bottom. They generally do not freeze, although there are some exceptions to this rule.
Always keep essential oils in cool temperatures, around 5° Celsius. They should be stored in dark glass containers that are tightly capped or sealed to stop evaporation and prevent oxidation. This will ensure they will keep their therapeutic properties for the length of their shelf life.
Essential oils must be kept away from direct sunlight and heat to prevent photocatalytic activity. When purchasing essential oils from a shop it is important to look out for where and how they are stored.
Essential oils are obtained from various parts of a plant including leaves (Thyme), roots (Ginger), seeds (Coriander), flowers (Chamomile), wood (Sandalwood), fruit (Grapefruit) and bark (Cinnamon).