The incidence of allergic contact dermatitis to essential oils is rising as these compounds are found in a wide range of products.1 They are a common ingredient in cosmetic products, together with fragrances, and sensitization to both is common.2 Sensitization to essential oils and fragrances can be accurately diagnosed by patch testing with fragrance markers from the standard series of allergens of the Spanish Contact Dermatitis and Skin Allergy Research Group (GEIDAC), markers from specific allergen series, and products brought in by the patient.3 A 58-year-old man with a history of psoriasis being treated with topical corticosteroids and emollients presented with edema and erythema on both eyelids that had appeared 24hours after fumigating a vegetable plot with a homemade fumigation mix. The cutaneous manifestations disappeared with the application of topical clobetasol propionate. The fumigation mix contained pure neem oil bought from an online distributor (Fig. 1). The patient reported that he had used neem oil as an emollient for psoriasis plaques in the past. The plaques disappeared, but the man developed eczematous lesions after repeated applications and decided to stop using the oil. The lesions cleared when he did this. We performed patch tests with the GEIDAC standard series, the Chemotechnique Diagnostics Fragrance Series, limonene hydroperoxide, linalool, and neem oil (brought in by the patient). Readings at 48 and 96hours were positive for nickel (++) and neem oil (+++) (Fig. 1B). Dilutions at 25% and 50% were also positive at 48 and 96hours (Fig. 1C). The same tests in 16 controls were negative. The patient applied neem oil to his forearm and developed an eczematous reaction at the application site and on both eyelids at 48hours. Based on these findings, we established a diagnosis of airborne allergic contact dermatitis to neem oil in a patient who had already exhibited manifestations of allergic contact dermatitis to the same substance. Neem oil is extracted from the seeds of the neem tree (Azadirachta indica), which is native to India and has been widely used in Hindu medicine for years. The neem tree has anti-infective, immunomodulatory, anti-inflammatory, antioxidant, and anticarcinogenic properties and has been used to treat many systemic and dermatological diseases, including alopecia, ulcers, leprosy, acne, psoriasis, eczema, ringworm, warts, and radiodermatitis.4,5 It is also used in cosmetic products, pesticides, fungicides, insect repellents, and fertilizers.6 Just 4 cases of contact dermatitis to neem oil have been reported and they have all involved different diseases treated topically. Two of the patients had psoriasis7,8 (like our patient), 1 had alopecia areata,6 and 1 had a boil.7 In the cases described by Greenblatt et al.7 and Lauriola and Corrazza,8 the same tests performed in 5 and 8 controls, respectively, were negative. Only one of the studies cited, that of Hamamoto, tested diluted forms and these were positive.7 Two of the patients tested positive to other fragrances (fragrance mix I and other essential oils contained in the patients’ own products).6,8 Our patient only tested positive to neem oil. The allergen in neem oil is unknown as over 140 components have been isolated.8 Of these, triterpenoids (azadirachtin and nimbin), coumarins, contaminants, and oxidation subproducts all have allergenic potential. Components may also be altered during the oil extraction process. Products with a high concentration of azadirachtin are potent pesticides but they can also act as irritants. It is therefore important to perform a complete study with dilutions and controls to rule out irritant contact dermatitis.7 The current case highlights the importance of thoroughly questioning patients with suspected allergic contact dermatitis. It is important to obtain information about the products the patients are exposed to in different areas of their lives, including hobbies and the use of alternative treatments, perhaps even for another condition.

Figure 1.

A, Neem oil. B, Patch test results at 96h for neem oil (+++). C, Patch test results at 96h for dilutions at 25% and 50%.

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