Before we talk about where I buy my essential oils, I think it’s important to discuss two terms often used in the buying controversy: “therapeutic grade” and “certified pure therapeutic grade”. It’s important to note that there is no agency that regulates these terms, rather they are made up by the essential oil industry. Don’t let these terms fool you or effect your buying.
There is an immense amount of studies exploring the concerns that essential oils are highly concentrated and can irritate the skin when used in undiluted form.[26][27] Therefore, they are normally diluted with a carrier oil for topical application, such as jojoba oil, olive oil, or coconut oil. Phototoxic reactions may occur with citrus peel oils such as lemon or lime.[28] Also, many essential oils have chemical components that are sensitisers (meaning that they will, after a number of uses, cause reactions on the skin, and more so in the rest of the body). Chemical composition of essential oils could be affected by herbicides if the original plants are cultivated versus wild-harvested.[29][30] Some oils can be toxic to some domestic animals, with cats being particularly prone.[31]
Young children and the elderly may be more sensitive to essential oils. So you may need to dilute them more. And you should totally avoid some oils, like birch and wintergreen. In even small amounts, those may cause serious problems in kids 6 or younger because they contain a chemical called methyl salicylate. Don’t use essential oils on a baby unless your pediatrician says it’s OK.

This is one of the most vital things you must know about essential oils: not all essential oils are created equal. In fact, most of them are worthless to your health and often synthetic. Therefore, when buying such oils — whether 5ml, 10ml or 15ml bottles — choose pure ones that are certified USDA organic, 100 percent pure, therapeutic grade and indigenously sourced.
“An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are generally extracted by distillation, often by using steam. Some important information that you should know about an essential oil is the botanical name, chemotype (if applicable), origin of plant (this can drastically change the chemical constituents percentages) and extraction method.” (source)
The inhaled aroma from these "essential" oils is widely believed to stimulate brain function. Essential oils can also be absorbed through the skin, where they travel through the bloodstream and can promote whole-body healing. A form of alternative medicine, aromatherapy is gaining momentum. It is used for a variety of applications, including pain relief, mood enhancement and increased cognitive function.