Before applying essential oils to your skin you should always dilute them in a carrier oil such as olive oil or apricot kernel oil. The amount of dilution will vary depending on the application and on which essential oil is being used but a general guideline is 1-3 drops of essential oil to every teaspoon of the carrier oil. In the past I used tea tree and lavender essential oils undiluted but after some research I have decided not to make any exceptions. Undiluted (also called "neat") application of even tree tree or lavender essential oil may cause certain individuals to develop a rash and become sensitized to that particular oil. Human skin is highly absorbent so when you apply essential oils to your skin you absorb them into your body. This is yet another reason not to use large amounts of essential oils on your body at one time. There are some concerns in the herbal community that prolonged use, especially of undiluted essential oils, may cause liver damage.
I don't suggest keeping any herbs or herbal preparations within the reach of small children but this precaution is especially vital when it comes to essential oils. If a child grabs a few peppermint leaves and tastes them, it isn't too likely to cause serious damage but if a child puts undiluted peppermint essential oil in his or her mouth it could have very serious results and even result in hospitalization.