Why are some oils phototoxic?

When we learn aromatherapy, we should be taught about the phototoxicity of certain essential oils but what does this really mean and why do some oils react to direct sunlight when applied topically? This article intends to explain these facts as well as showing definitively which oils to avoid in the sun and what this means for the practising aromatherapist.

What is phototoxicity?

According to Dijoux et al. 2006, "Phototoxicity is a skin reaction caused by concurrent topical or systemic exposure to specific molecule and ultraviolet radiation. Most phototoxic compounds absorb energy particularly from UVA light leading to the generation of activated derivatives which can induce cellular damage". So to put this in layman's terms, we are talking about burning of and damaging the skin after applying a specific essential oil (in the context of this article), following exposure to the sun, tanning beds or heat lamps - basically exposure to any form of Ultraviolet UVA light. The effects of photosensitisation include reddening of the skin (erythema), burning and blistering and inflammation of the skin.

Of all the essential oils we learn about, Bergamot (Citrus bergamia L.) is cited as being the most phototoxic. Over 90% of the whole oil, which is distilled from the epicarp and mesocarp of the fresh fruit, consists of volatile monoterpene hydrocarbons, alcohols and esters. A non-volatile fraction consists of 4-7% coumarins and psoralens (Phytotherapy Research, 2014). Bergamot contains a furocoumarin by the name of Bergapten, which is biologically active and induces a lethal and mutagenic photosensitisation of bacteria and "lethal and clastogenic effects on mammalian cells in tissue cultures (Ashwood-Smith et al., 1980 cited by Cosento et al.). Bergamot contains about 2% coumarin-psoralens. As a result, some essential oil suppliers have created bergapten free Bergamot oil (FCF), but does this make any difference to the therapeutic effects? It is certainly important in the perfume industry but as clinical aromatherapists or essential oil therapists, we can use the whole natural plant with cautions. Bergamot oil typically is absorbed by the skin within 40-60 minutes (Schilcher 1985) so it is important to warn clients if you have used Bergamot oil that is not FCF to avoid exposing their skin to the sun for at least an hour after application, although Tisserand advises that these essential oils can produce a phototoxic reaction for up to 12-18 hours after application but does not state why - perhaps it is best to always err on the side of caution. In tests carried out, skin pigmentation at the application site with 10% dilution of Bergamot oil that had been irradiated still showed after 23 days (Marzulli and Maibach 1970). The best course of action would be to avoid using phototoxic oils altogether or to use extremely low dilutions of around 0.5 to 1% (1-2 drops in 10mls of base product). The other option is to cover the area after application to protect it from UV rays.

This image shows the testing on human skin of 1% dilution of bergamot oil after 20 minutes and 40 minutes after exposure to UVA light.

In the cosmetic and perfume industry, where essential oils are used, it is important that assessments are conducted to calculate potential phototoxic hazards and you can find the International Fragrance Association guidance on this at http://www.ifraorg.org/en-us/standards-library/s/phototoxicity. Clearly in perfume there is a real issue if natural essential oils are being used whereas there is no phototoxic problem if the oils are used in products such as soaps and shampoos that are immediately washed off the skin.

Lemon oil also contains furocoumarin derivatives and is known to cause phototoxicity. In a study where the oil was fractionated, it was found that the phototoxic culprits are oxypeucedanin and bergapten (Naganuma et al., 1985), although the actual ratios varied depended on where the plants were grown in the world. Lime oil and Bitter Orange oil was also found to contain oxypeucedanin but although this does elicit photopigmentation, it does not cause visible erythema as does bergapten. So the way in which the essential oil is extracted is important. If the oil is cold pressed, the non-volatile furocoumarins will be present but if the oil is optained via steam distillation, then only the volatile compounds will be extracted. In further studies, phototoxic responses were found to be in the Rutaceae and Umbelliferae (now renamed Asteraceae in 1997) families, with the exception of Verbenaceae (Forbes et al. 1977). However, not all citrus oils are phototoxic.

Some people have been incorrectly taught that Lavender oil is phototoxic. Tisserand and Balacs (1995), have confirmed that whilst Lavandula angustifolia L. can cause mild sensitisation and irritation, it is definitely not phototoxic and does not contain furocoumarins. I have also recently read a blog where an aromatherapist was telling students that Mandarin essential oil (Citrus reticulata L.) was phototoxic when again it most certainly is not; however, Mandarin Leaf is. Similary, Sweet Orange (Citrus sinensis L.) is absolutely fine to use whereas cold pressed Bitter Orange is not. Tisserand has produced a valuable table showing which oils are in fact photo-toxic and if you stick to this, you will be fine. In all cases, where you do use any of these oils, be mindful of what your client will be doing immediately after the treatment. For example, do not give a bald man a lovely face and head massage with Bergamot oil on a sunny day and do not use phototoxic oils in face or hand creams, especially in the summer or if you are practising in warmer climates than we experience here in the UK. As stated above, either avoid the use of phototoxic oils or give your clients clear safety aftercare advice. So the moral of this story is yes you can use these oils containing furocoumarins, but use them in low dilutions and give proper aftercare advice to your clients. Also, ensure you keep up to date with current essential oil information so that as a practitioner, you serve the very best needs of your clients.

If you would like to train with me as an aromatherapist or as an essential oil practitioner if you would prefer not to learn the massage component required for aromatherapy, we offer these diplomas through Complementary Health Professionals. Please click on the course list which you can access here and follow the links through to read the entire syllabus. These courses are delivered via a blended learning programme, which means you have the convenience of learning the theory at home in your own time fully supported by me as your personal tutor and our online education centre that is packed full of great resources to make your learning informative and interesting. Then you will need to attend day workshops with me in London or Kettering, where I will support your development of practical skills in massage and blending. For the essential oil diploma, this is all online but I do hold Advanced Blending Master classes in the year that you can come along to in order to help develop your blending skills. We also have a yearly aromatic tour of Kew Gardens in June each year, which is great fun as well as being educational.

Once qualified with us, you can join our professional association, gain insurance and set up in practice. If you are a therapist, why not join our therapy family? We have excellent membership benefits for all therapies. Click here for details of membership packages.