Special note regarding Essential Oils: Essential oils are safe when used externally in low concentrations (no higher than 5%) To err on the side of caution, In my formulations which include essential oils I keep my concentrations between 1 and 4%.
A small proportion of people may experience skin irritation, allergic reactions, or cross-sensitivity to essential oils. Cross-sensitivity is the potential for an allergic reaction to similar substances (for example, if you are allergic to ragweed, you might also be allergic to chamomile essential oils). Irritation is characterized by a rapid onset redness and pain in the skin exposed to the essential oil. It can occur with the first exposure. The skin generally heals without long-term problems, but you probably would not want to use the essential oil that caused the irritation again.
If you are someone who is taking a lot of prescription medication and/or has a lot of allergies, you should do a patch test by following the instructions below to check for skin irritation and sensitivity before using a product which contains essential oil.
How to Perform a Patch Test: Using the inside of the forearm, apply a small amount of product to the pad of a bandaid and keep the bandage on the skin for 48 hours. After 48 hours remove the bandage and check for irritation. If the skin under or around the bandage becomes red, swollen, itchy, or develops blisters, that is a reaction and you should avoid skin exposure to the essential oil in the product you are You may repeat to check for allergic sensitivity. Remember, however, that allergies can develop any time after the first exposure; thus absence of a reaction does not necessarily mean that an allergy will not develop with further exposure)