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Authors: Dr Fathima Ferial Ismail, Dermatology Research Fellow, Sinclair Dermatology, East Melbourne, VIC, Australia; A/Prof. Rosemary L Nixon, Dermatologist and Occupational Physician, Occupational Dermatology Research and Education Centre, Skin and Cancer Foundation Inc., Melbourne, VIC, Australia. Technical editor: Mary Elaine Luther, medical student, Ross University School of Medicine. DermNet NZ Editor in Chief: Adjunct A/Prof. Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. January 2020.
Essential oils are volatile aromatic substances obtained from plant material through various methods including distillation and extraction. Essential oils have been widely used for centuries in aromatherapy, balneotherapy, and perfumery (see perfumes and fragrances). During aromatherapy, essential oils are often applied directly to the skin or delivered by inhalational methods. Essential oils are also increasingly being used in household products and in aerosol diffusers [1,2].
Commonly used essential oils include [1,3]:
A number of essential oils are known to be allergenic. Essential oils that commonly cause allergic contact dermatitis include [1–3]:
Allergic contact dermatitis to essential oils occurs more commonly in people with occupational exposure to essential oils [1,5,6]:
Other groups who risk allergic contact dermatitis to essential oils include [1,6]:
As a result of increasing use of essential oils in the home, there have been cases of airborne contact dermatitis caused by fragrance diffusers [7,8].
Essential oils are used in many countries such as Iran, India, China, and Thailand as a traditional topical therapy for stomach-ache and flatulence in infants. Localised eczematous reactions have been observed in the abdominal region of infants exposed to this therapy .
Allergic contact dermatitis is a delayed (type 4) hypersensitivity reaction that generally occurs 24–72 hours following exposure to an allergen. The mechanism involves recognition of the allergen by pre-sensitised T-lymphocytes, which release inflammatory cytokines that activate the skin immune system and cause dermatitis .
Each essential oil can have over 100 constituents . Often people with allergic contact dermatitis to essential oils react to many different oils, not just one, presumably because of shared constituents .
The most common symptoms of allergic contact dermatitis are skin itching, redness, and scaling . These symptoms usually occur at the site of contact with the essential oil but can extend outside of this area.
In aromatherapists, the hands and forearms are most commonly affected with possible involvement of the face, neck, and legs [5,11,12]. Spread to other areas has also been reported . Symptoms usually improve with time spent away from work.
People who have been exposed to airborne essential oils can also have widespread involvement [7,8].
People who work within the aromatherapy and massage industry can experience serious consequences of sensitisation to essential oils, which can result in them being unable to work . There can also be an impact on social activities and even permanent disability .
A detailed history of exposure, together with the clinical features, morphology, and distribution of the lesions, are important in making the diagnosis of allergic contact dermatitis to essential oils.
In cases of occupational exposure to essential oils, symptoms often improve during holidays or weekends .
Patch testing is used to determine the cause of allergic contact dermatitis. Patches containing small amounts of potential allergens are applied to the back and then removed after 48 hours to observe for an allergic reaction, which manifests as localised eczema. The test site is observed again after an additional 48–96 hours .
Patients who are allergic to essential oils commonly have multiple sensitisations . Most patients with allergic contact dermatitis to essential oils also have positive reactions to fragrance mix I in the baseline series; however, extended patch testing is necessary, because not all affected patients are positive to fragrance mix I . Patch testing to the patient's own products is useful as the allergen may be an oxidised component .
Gas chromatography and mass spectrometry have been used experimentally to analyse essential oils in order to identify common allergens within them .
Conditions that may co-exist or be confused with allergic contact dermatitis to essential oils are:
Irritant contact dermatitis to essential oils in high concentrations can coexist with allergic contact dermatitis. Irritant contact dermatitis is confined to the area of contact with the offending substance, whereas allergic contact dermatitis can extend beyond the area of direct contact .
Contact urticaria presents as a weal-and-flare reaction within minutes of exposure to a substance and resolves within minutes to hours .
Prevention of allergic contact dermatitis to essential oils relies on allergen avoidance . In particular, people should be advised not to apply neat, undiluted oils directly to the skin, as this can lead to sensitisation .
Avoidance of the allergenic essential oils usually results in resolution of skin symptoms . In some cases, the symptoms persist and become chronic, especially if there is ongoing inadvertent low-dose exposure in daily life.
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