Essential oils can be sensitising. It is necessary to conduct a patch test before purchasing them to make sure it suits your skin type. Some of these oils cause severe skin sensitising. So if you have a sensitive skin, it's always advisable to check with a qualified practitioner first.
Make sure that the product is 100% pure and natural. Non-organic brands may add fillers which often include harmful chemicals that harms you in the long run.
Dilute essential oils prior to application. Essential oils can be blended with base oils or carrier oils before applying. They are highly concentrated and should not be used undiluted on the skin. It needs to be mixed with carrier/base oil. The ratio should be 3-4 drops of essential oil in 10ml of base oil. Some oils like olive, almond, jojoba, grape seed and coconut oil can be used as carrier oil.
Always store essential oils in a cool, dark place and out of direct sunlight. This helps to preserve their potency. Essential oils have a long shelf life, if stored correctly, some even last for years.