Essential Oils come in four different grades;
Synthetic, Fragrance Grade, Food Grade, and Therapeutic Grade.
Synthetic Grade oils are created in a laboratory.
Fragrance Grade oils are used to add fragrance to soaps, candles, perfumes, lotions, shampoos, etc. and usually has synthetic ingredients.
Food Grade oils are used as a flavoring in food, toothpaste, gum, candy, etc. and usually is done by high heat distillation.
Therapeutic Grades oils are pure, medicinal, steam-distilled essential oils and these are what Young Living oils are. They use a distilling process to preserve the integrity of the oil just as it is found in nature. Therapeutic grade oils can be used to penetrate cell membranes and enhance cellular function.
Care should be taken to ensure you use whichever type of oil you have for the indented purpose.Do not use a lesser grade oil or cheaper oil for what you had used a Young Living oil for. Not all oils are created equally. Lesser or adulterated oils can be very detrimental and could cause rashes, burns, and other skin irritations.
Do your research yourself to see what your oil company's testing requirements are and what they do with batches that do not meet standards.
I personally only want the best for my family and have found that with Young Living Essential Oils.
(Information taken from the Essential Oils Desk Reference and an Oil Presentation by Krista Wiggington.)