The majority of essential oils are perfectly safe when used on the skin in the dilutions used by most aromatherapists, i.e. 3% or occasionally 4% for most massage blends, with lower dilutions for children and people with sensitive skin, or when using oils that are known to be potentially somewhat irritant, use 1 % or even as little as 1 % in such instances. See our article on Dilution Rates for more information.

Some oils have such an ability to irritate that they must never be used on the skin, even in dilution, and not surprisingly a number of these are derived from 'hot' spice plants. Some of these, such as Horseradish and Mustard are hardly ever included in lists of essential oils offered for sale, but one or two others, including Clove (Bud, Stem and Leaf) and Cinnamon (Bark and Leaf) may be listed because they have some important uses in inhalations and vaporisations.

Different parts of the same plant may be less or more irritant and there are also variations between different varieties of the same species. For example, Cinnamon Leaf is somewhat less irritant than Cinnamon Bud, while Dwarf Pine is highly irritant and not to be used at all on the skin, while Scotch Pine is among the least irritant oils. Most citrus oils are mildly irritant, but Lemon seems to be more aggressive than any other, and oils with a 'Lemon' scent, though not from the citrus group, such as Lemongrass, Lemon Verbena and Melissa also needed to be used with caution.

Obviously, as suggested in the first paragraph, different people will react differently to potential irritants, and people with ultra­sensitive skins (often very fair people or redheads) may experience irritation from oils that are not usually regarded as likely to do this. Common sense and caution should go hand in hand when deciding on the choice of oils and strength of dilution. Irritation is more likely to arise from the use of oils in the bath than during massage, if the oils are used undiluted for bathing. For most oils, and for many people, 6 drops of undiluted oil in the bath is quite safe, but anybody with a sensitive skin should dilute all oils in a carrier before using them for bathing, and oils known to be mildly irritant should be restricted to not more than 3 drops in a bath, whoever is using them.

Occasionally, oils with a very mild irritant effect are used deliberately to produce reddening of the skin in a controlled and beneficial way. Such oils are described as rubefacient (i.e. reddening) and they produce a sensation of warmth, and increased local circulation which can be very comforting and healing in painful muscular conditions, rheumatism, etc. The most useful of the rubefacient oils are Black Pepper, Juniper, Marjoram and Rosemary.

If you are not sure if you may be sensitive to certain oils, always do a skin patch test first.