Some essential oils can cause irritation. Even essential oils that have been actively promoted as being remarkably safe to use.
Prior to using an essential oil for the first time, skin patch testing is often recommended as a method of determining if you have an existing sensitivity/irritation to the natural constituents present in a particular essential oil.

There are some simple rules to follow when evaluating a scent:
• Do not place your nose right up to the open tester and sniff. The undiluted oil is incredibly strong and can give you a headache. Instead, hold the lid at least five inches from your nose and gently sniff.
• Never use essential oils undiluted on the skin.
• Avoid using essential oils that are hazardous and that are known to be of higher risk in causing dermal irritation.
• Place 1-2 drops of a diluted skin safe essential oil on your inner forearm or back as the most appropriate regions for testing.
• Apply a bandage. Do not get this area wet during the test.
• If you feel the onset of any irritation or if any reaction occurs, immediately remove the bandage and carefully wash the area with mild soap and water.
• If no irritation occurs after 48 hours, the essential oil, should be safe for you to use diluted on your skin.
• Also keep in mind that if you are allergic to a particular plant, you are more likely to be allergic to that botanical’s essential oil.
• When comparing a variety of oils, take a break in between scents. Sniffing oils too closely together can overwhelm the senses and reduce your ability to discern the fragrant notes.