Most of these essential oils are strong in nature and can cause side effects, if they are not used in appropriate manner and quantities, therefore you should consult a medical practitioner before using these essential oils. Most Should be used with a base / carrier oil.

What is an Essential Oil?
An essential oil is a concentrated, hydrophobic liquid containing volatile aroma compounds from plants. They are also known as volatile or ethereal oils, or simply as the "oil of" the plant material from which they were extracted, such as oil of clove. An oil is "essential" in the sense that it carries a distinctive scent, or essence, of the plant