Although generally safe there are some safety concerns associated with Essential Oils including Phototoxicity, also called Photosensitization.

Have you seen the precaution - If applied to the skin avoid sunlight or UV rays (including sun beds) for 12 hours or something similar on some essential oils or essential oil blends and wondered what this was all about?

Phototoxicity is a reaction that can occurs on the skin when it is exposed to sunlight (or UV rays) in the presence of certain chemicals. The most common phototoxic agents are psoralens, or furocoumarins. These polycyclic molecules have a structure that gives them the ability to absorb ultra violet photons, store them for a while and then release them in a burst on to the skin.

The reaction will only occur if the sensitizing agent is present on the skin when it is exposed to Ultra Violet light and can take the form of a mild color change all the way through to deep weeping burns. Sometimes the skin is able to revert back to normal over time, but at other times the reaction can be permanent. The reaction can occur almost immediately, or it can be delayed and only occur following a period of sensitazation.

Only a few essential oils contain these phototoxic components and while it is usually in amounts of less than 2%, even at this low level and even when the oil is diluted down with a carrier to a 1 - 3% dilution, they are still often capable of producing phototoxic effects if the skin is then exposed to sunlight or UV rays. If these essential oils were to be used undiluted or if the skin were to be exposed to concentrated UV light or strong sunlight then a very severe phototoxic effect could occur.

Expressed Bergamot essential oil has been found to be one of the more phototoxic essential oils. It is an oil that has been used extensively in perfumes (especially eau de cologne), creams, lotions and soaps. Studies in the 1950s and 60s showed that, in the presence of UV light, a reaction took place between furanocoumarins and the skin. In France in 1970 J Meyer reported problems with a tanning lotion containing bergamot essential oil, and in 1972 Urbach & Forbes reported that severe phototoxic effects were experienced when humans were treated with expressed bergamot oil and stimulated sunlight. A number of other studies have confirmed the photoxicity of express bergamot oil. The bergapteen (a furocoumarin) in bergamot oil was found to produce abnormally dark pigmentation and reddening of the surrounding skin after exposure to an ultraviolet lamp. This condition is called berloque dermatitis, or bergapten dermatitis. The patches of darkened skin characteristic of this condition can remain for many years.

As mentioned above it is the furocoumarin bergapten present in bergamot expressed essential oil that causes the reaction. Today one is able to purchase an essential oil of bergamot that has been rectified to remove this furocoumarin - known as Bergamot FCF while this is certainly a much safer oil to use on the skin as it does not contain the phototoxic chemical, many find that its aroma is inferior to the aroma of expressed Bergamot oil.

The risk of phototoxicity when using some essential oils not only depends on the presence of a furocoumarin but also the type of furocoumarin and how much of it is present.

When citrus essential oils are extracted by expression (a process where the skin of the fruit is punctured and the essential oil is released), all the chemical components present in essential oil in the skin of the fruit come across into the essential oil collected including the furocoumarins which are fairly large components. However furocoumarins are physically too large to make it across a steam distillation process so when citrus essential oils are produced by steam distillation there is no longer the problem of phototoxicity.

Essential Oils that are strongly phototoxic include:

• Expressed Bergamot
• Lemon Verbena
• Taget
• Expressed Lime
• Rue
• Opopanax

Essential oils that are moderately phototoxic include:

• Expressed Orange, Bitter
• Expressed Lemon
• Cumin

Essential Oils that are mildly phototoxic include:

• Angelic Root
• Caraway
• Cassia
• Cinnamon Bark

Citrus Essential oils that are Not phototoxic include:

• Bergamot FCF (bergaptene free)
• Lemon - steam distilled
• Lime - steam distilled

There exists a bit of disagreement on some of the classifications on phototoxicity: Expressed grapefruit is classified as moderately phototoxic by one source and mildly phototoxic by another.
Expressed mandarin is classified as moderately phototoxic by one source and not phototoxic by another.
Expressed Orange, sweet is classified as not phototoxic by one source, but Orange (unspecified sweet or bitter) is classified as moderately phototoxic by another source.

I would suggest that when in doubt exercise caution and consider that all expressed citrus oils could be phototoxic while steam distilled citrus oils, or bergamot FCF are not.

Also keep in mind that as phototoxicity or photosensitization is a reaction that takes place between the skin and the phototoxic component in the essential oil, inhalation of the oil doesn't usually cause the same reaction.