What constitutes a dermal or skin reaction to essential oils? There are actually three types of dermal toxicity: irritation, sensitization and phototoxicity. All three are considered forms of dermal toxicity that every aromatherpist as well as lay users of essential oils should know about and recognize. Here is a brief description of each.


Reactions come from compounds in a Essential Oils that react with cellular components of skin resulting in a reddening of the skin in varying degrees. This reddening of the skin occurs almost immediately. Oils that can cause skin irritation include phenols found in oregano, savory, thyme, and clove, or an aromatic aldehyde found in cinnamon, and cassia. The reaction is usually heat and burning and is not an allergic reaction. It comes from too much oil in a given skin area. It can also be caused by adulterated oils. Treatment for skin irritation is an immediate dilution with a carrier oil to quench it. This usually takes care of the redness and burning.


In sensitization, compounds within an essential oil cause an activation of the immune system. The result is a contact dermatitis. At the first exposure, usually nothing happens. In subsequent exposures, reactions occur. Reactions can be in the form of a rash, sneezing, shortness of breath or hives. Fragrance allergy is the most common cause of cosmetic contact dermatitis. The most sensitizing component of commonly used essential oils is cinnamic aldehyde from cinnamon oil. Eugenol in clove oil is also sensitizing. Other essential oils that pose a lesser risk include tea tree, lemongrass and ylang ylang. It is important to remember that any concentration of an oil may sensitize skin in a person with a genetic pre-disposition. Allergic reactions such as this usually develop in people who already manifest allergic reactions of one kind or another-asthma, eczema, and nasal allergies. How would you treat a skin sensitization reaction? You might try one of the anti-inflammatory essential oils like Roman chamomile or lavender in a 10% dilution.

If someone knows they have sensitive skin, a patch test should be done first. Dilute the essential oil to double the concentration to be used and put it on an adhesive bandage. Place the bandage on the person’s forearm and leave in place for 12-24 hours to assess any adverse reactions.

Some causes of sensitization:

o Adulterants in an oil

o Some reactions can take years to build up

o Taking several medications at the same time may show a sensitivity to essential oils

o Sometimes a mixture of a chemical and an essential oil can trigger an allergic reaction (for example spraying the garden with a pesticide then using an essential oil on the skin)

o Interaction of the essential oil with residues of synthetic, petroleum-based personal care products-Compounds found in hand creams, mouthwashes, shampoos, antiperspirants, after-shave lotions and hair care products

Benzalkonium chloride

Sodium lauryl sulfate

Propylene glycol

Aluminum salts

Methylene chloride

Methyl isobutyl ketone

Methyl ethyl ketone


Phototoxicity is an interaction between a component in an essential oil, the skin, and ultraviolet photons resulting in a skin reaction. These reactions can vary from pigmentation of the skin to severe full-thickness burns. The most common phototoxic agents are psoralens and furanocoumarins. Their chemical structure absorbs the energy from UV rays (sunlight or tanning beds) and then releases the energy in a burst to surrounding skin cells resulting in brown spots or burns. Usually keeping away from the sun for 12 hours after application is sufficient to prevent these reactions. It is sometimes said that all citrus oils are phototoxic, but this not true. When the citrus oils are steam distilled, none are photo-toxic. However, distilled citrus oils are rarely used in aromatherapy because they are less aromatic and don’t have the same therapeutic qualities as the expressed citrus oils do. The steam distilled citrus oils are mainly used for flavorings.

The common essential oils considered phototoxic include: bergamot, lime, bitter orange, lemon, rue, angelica root, petitgrain, rue and grapefruit. Some authorities also include lemongrass, cumin, fennel, anise, and verbena absolute on the list. The bottom of the feet is one of the safest and most effective places to use essential oils. According to Tisserand and Balacs in Essential Oil Safety, the expressed oils of mandarin, sweet orange, tangelo and tangerine are not phototoxic. This is due to the quenching effects of other compounds, especially sesquiterpenes that make the unruly furanocoumarins behave. Myrrh is a perfect example. It contains at least ten types of furanoid compound (20-27%)-more than any other oil, yet it is not phototoxic. In ancient times, they actually used myrrh oil on the skin daily without sunburn reactions.