According to the American College of Healthcare Sciences, performing a skin patch test is as follows:
Wash and dry your forearm, specifically in the crook of your arm, thoroughly with unscented soap.
Apply 1-drop of the oil onto the crook of your arm. When using diluted essential oils, place enough of the oil & base blend to moisten, but not saturate and cover with sterile gauze.
Close your arm for five minutes.
Open and close the arm one more time.
Check for a reaction after 24 hours.
For undiluted essential oil, test the area using this process a second time. Should a reaction present itself, wash the area with unscented soap and water, or milk. Reactions can vary from simple redness on the area to painful rashes or asthma attacks.
Testing for sensitivity is an imperative part of an Aromatherapist’s safety protocols and should be incorporated into an essential oil user's repertoire. An irritation presents itself immediately, whereas sensitization can present itself in many forms over 12 to 21 days. Irritants are surface responses to a stimulant, in this case, the application of essential oils. An allergic reaction is a biochemical response to repeated exposures. A skin patch test is extremely effective in identifying irritants, which prevent long term allergic reactions. Redness in the area where a skin patch test was performed may only indicate a minor irritation, which over a period of 21 days of use creates an extreme allergic reaction such as asthma and circulatory issues. A skin test allows you to use essential oils within your body's limitations. As with any therapeutic grade essential oil or medicinal herb, use and applications are very personal and should always be treated as fresh individual cases.
Once you evaluate the results of your skin patch test it is possible to dilute the essential oil for use without igniting an allergic reaction, nor flaming an irritation. Once an irritation has been identified, however, a skin patch test should be performed using each proposed dilution to ensure safe future use. While this may cause some impatience, the time and effort are worth keeping yourself safe and healthy.
Petersen, BA, Dip-NT, Dip-Acu, RH, D. (2014). Aroma 101: Introduction to Aromatherapy. Portland, OR: American College of Healthcare Sciences.
Petersen, BA, Dip-NT, Dip-Acu, RH, D. (2015). Aroma 203: Aromatherapy I. Portland, OR: American College of Healthcare Sciences.