Essential oils are highly concentrated liquids and only a few of them are safe to use neat such as Lavender oil or Tea tree oil on burns, insect bites, cuts and grazes. 

For most of the time essential oils are mixed with a carrier oil to dilute them in order to apply to the skin safely.

Essential oils are usually diluted 3% (That's 3 drops of essential oils to every 100 drops of carrier oil - 100 drops is approximately 5mls).

For babies, children, pregnant women, frail elderly and those with sensitive skin should dilute the essential oils further to 0.5% - 1.5%.  Please note that there are some essential oils that are not recommended for this group and other illnesses such as heart conditions or epilepsy therefore always check the contra indications on any essential oils before using.

When essential oils are added to water this does not dilute them as water and oil do not mix, so when you add a few drops to a bath most of the oil will settle on the surface and on the skin undiluted.  It is important to remember when dealing with skin irritant or photosensitising oils. If you want to dilute essential oils to water it must be first be diluted in alcohol then added or add a pre blended massage oil.