Essential oils are common in natural skin care products and contribute with fragrance as well as other positive properties. Also popular are natural perfumes, containing ready-made blends of essential oils to be worn on the wrist with various stress-relieving, reviving or energizing effects. To add a few drops of essential oils to your DIY products is also fun. You have to be careful though, about which essential oils you choose and thoroughly check the content of the ready-made blends, especially when it comes to products intended to be used on parts of the body that might be exposed to sunlight. If you are not, you risk serious allergy reactions and burns.

Why Are Some Essential Oils Phototoxic?

Certain essential oils contain phototoxic substances that can cause severe allergic reactions and even burns if they are exposed to UV-light. Inflammation, blisters and red, burnt skin are usual reactions. These oils contain furocoumarins (also called furanocoumarins), a group of substances that binds to the DNA in the skin cells. When exposed to UV-light, they elicit a reaction that damage the skin cells and cause a severe allergic reaction. Depending on the concentration, furocoumarins can in the presence of UV-light result in up to third-degree burns. In one case, a couple of drops of essential lemon oil in a bowl in the sauna was enough to cause burns on a woman when she used a tanning bed immediately after. It is recommended to avoid sun exposure and tanning beds for up to 12-18 hours after using furocoumarin containing oils on the skin. The effect is delayed and burns can develop up to 36-72 hours after and cause a discoloration that lasts for months. What is more, even skin contact with fresh citrus fruits in the sun can lead to burns. Numerous case reports concerning lime have gifted this syndrome with the name "Margarita photodermatitis".

Which Essential Oils Contain Furocoumarins?
Furocoumarins are found in many citrus fruits and a few other plants. However, not all citrus fruits contain furocoumarins. Essential oils from lemon and lime peel, for example, are highly phototoxic while orange and mandarin are not. Also, essential oils extracted from other parts of citrus plants than the fruit peel, such as leaves and flowers, usually contain much lower levels of furocoumarins and the oils are therefore not phototoxic. Examples are neroli and petitgrain oils, extracted from the flowers and leaves and twigs, respectively, of the bitter orange tree. These oils are OK to use in the sun while oil from the fruit peel of bitter orange is highly phototoxic. An exception is mandarin, where no part of the plant contains high levels of furocoumarins but where oil extracted particularly from the leaves still is phototoxic since it contains another phototoxic substance, namely, dimethyl anthranilate.

How much furocoumarins there are in a citrus peel essential oil also depend on the extraction method. Furocoumarins are heavy molecules that are less volatile than many of the other components in essential oils. This is why cold-pressed essential oil (also called expressed) from for example lemon is phototoxic while steam distilled is thereby OK to use in the sun without risk. Sometimes the furocoumarins are removed from the essential citrus oils after the extraction. Whatever method, when it comes to fragrance, the cold-pressed oils are considered superior since they have a more complete oil profile. For this reason, many companies market several versions of essential oils containing furocoumarins. Check for labels like ”steam distilled”, ”furocoumarins free (FCF)” or ”bergapten free” to be sure to obtain an oil that you can safely use in lip balms, skin moisturizers, perfumes or any other application intended to be used directly on the skin.

Reference

Tisserand, R. and Young, R., Essential Oil Safety: A Guide for Health Care Professionals. 2014: Churchill Livingstone/Elsevier.