Most essential oils are safe and free of adverse side effects when used properly. However, as with any substance you are introducing into your body, it is important to use them intelligently. We recommend that you never eat or drink essential oils. You should pay attention to the following factors.
DosageDose is the most important factor in essential oil safety. Some essential oils used in the wrong doses or too high a concentration have been found (in animal and laboratory studies) to contribute to tumor development and other harmful changes in the body. Some essential oils can even be damaging to the skin, liver and other organs if used improperly.
PuritySometimes essential oils are altered by adding synthetic chemicals or other, similar smelling, essential oils or they are sometimes diluted with vegetable oil. Look for language indicating purity on the label. It is not necessarily bad if the label indicates, for example, that the bottle contains 20% essential oil and 80% vegetable oil. This is sometimes done so that popular but expensive oils like rose or neroli (that can cost over $100 per teaspoon when pure) can be made more affordable. If you think you are starting with 100% essential oil and you are not, however, you may be disappointed with the results. On the other hand, if you are starting with professional quality essential oils, which are generally much more concentrated, you need to dilute them to be safe.
Application methodAn essential oil that is safe when applied in one way may not be safe when used in another way. Some oils are considered safe if inhaled, and yet may be irritating if applied to the skin in concentrations as low as 3-5%. Thyme, oregano, clove, and cinnamon bark essential oils are examples of this. Several of the citrus oils, such as bergamot, lemon, lime, orange, and angelica, can cause phototoxicity (severe burns or skin cancer) if there is exposure to natural sunlight or sun-bed radiation following skin applications, whereas this would not result from inhalation.
Be sure to clarify the recommended application method and concentration for the essential oil and intended use. And once again, don't ingest oils without professional guidance.
Possible drug interactionsThere is little published research on interactions between pharmaceutical drugs and essential oils. Given the complex chemistry of essential oils, however, it makes sense that this is possible or even likely. As with dietary supplements and herbs, it is important to discuss regular essential oil use with your healthcare provider and together assess any potential risks and benefits. For example, studies indicate that peppermint and eucalyptus oils increase the skin absorption of 5-fluorouracil, an anti-cancer drug (Abdullah et al 1996, Williams & Barry, 1989).