Allergic Contact Dermatitis to Coumarin in a Tinted Moisturiser Containing Melilotus officinalis (Sweet Clover) Extract.
Fragrance allergens are a major cause of allergic contact dermatitis (ACD) in patients with head and neck dermatitis [1], and can often be missed in an ingredient list as they may masquerade under a botanical name or are not specified [2]. We present a case of coumarin ACD caused by Melilotus officinalis (sweet clover) extract in a tinted moisturiser. A 31-year-old female with mild lifelong flexural atopic dermatitis developed facial dermatitis. This improved after using topical corticosteroid and tacrolimus ointments, switching to fragrance-free skin care products, and using mineral sunscreen. She suffered an acute major flare of severely itchy, erythematous, flaky facial dermatitis 3 days after applying full face makeup for a job interview. She continued wearing the same makeup. Systemic prednisolone and mycophenolate mofetil helped but were discontinued because of side effects. A trial of narrowband UVB phototherapy further flared her condition. Examination showed well demarcated facial lichenified erythematous plaques with no papules or pustules. There was significant post-inflammatory hyperpigmentation (Figure 1). Skin prick test was negative to pollens and house dust mite. IgE level was normal and ANA, ENA, dsDNA were negative. Patch testing was performed at our tertiary dermatology centre in Melbourne. Haptens were obtained from Chemotechnique Diagnostics (Vellinge, Sweden) and applied with Allergeaze patch test chambers (SmartPractice, Phoenix, Arizona, United States). The patient underwent testing with the Australian Baseline Series, as well as with cosmetics, fragrance, and sunscreen series. Additionally, 22 personal items were tested, and the patient underwent photo-patch testing with our sunscreen series. Results from patch testing are shown in Table 1. Photographs of the patient's skin reactions following the patch tests are not available. Benzophenone 3 (oxybenzone) 10.0% pet Benzophenone 3 10.0% pet with 5 J UVA Neg Neg Neg + Contained in her Blistex SPF30 lip balm which she had used previously Coumarin 5.0% pet Cinnamal 1.0% pet + ?+ + + Our patient was diagnosed with ACD to coumarin, which we believe to be present in the M. officinalis extract found in her tinted moisturiser. She also reacted to fragrance mix 2, which includes coumarin, and finally had photoallergy to benzophenone 3, contained in her lip balm used previously. Despite contacting the manufacturer, we were unable to obtain individual ingredients of the tinted moisturiser in a testable form for independent patch testing. After avoiding this moisturiser, she had no further flares of facial dermatitis and did not require ongoing systemic immunosuppression (Figure 2—after treatment). Coumarin (CAS number: 91-64-5) occurs naturally in fruits such as kiwi fruit and pineapple and is used in cosmetics as a fragrance [1]. It has been reported that 1.2%–6.8% of patients with fragrance contact allergy are allergic to coumarin [3]. In one study by Nardelli et al., 6% of patch tested patients reacted to fragrance mix II, which contains coumarin, and within the reactive population, 4.4% reacted to coumarin as an individual constituent [4]. Local lymph node assays have shown that the more impurities in coumarin, the higher the chance of skin sensitisation [3, 5]. In the European Union, coumarin is one of the 26 fragrances required to be listed in leave-on products at 10 ppm concentration and 100 ppm in rinse-off products [2, 6]. M. officinalis (sweet clover) extract is marketed as an astringent and soothing agent in cosmetics, and is also described as having oestrogen-like activity, inhibiting activities of elastase and lipase and promoting fibroblast production [7]. However, it is not widely recognised that M. officinalis extract contains coumarin as a plant secondary metabolite in mean concentrations of 0.3% but does not contain furocoumarins that may cause photosensitisation [8]. The reaction to coumarin (benzopyrone) and photoallergic reaction to benzophenone-3 (diaryl ketone) show no evidence of cross-sensitisation due to their significant structural difference. In-depth chemical analyses of plant extracts used in cosmetics are not always available, making it difficult for consumers to avoid low concentrations of coumarin or other potential allergens. In the United States, where Bare Minerals is based, products containing M. officinalis extract are featured as fragrance-free on the SkinSafe website [9]. In the Environmental Working Group (EWG) Skin Deep website, there is no overlap between the list of coumarin-containing products (3874) and that of M. officinalis products, with 23 cosmetic products listed as fragrance-free [10]. Therefore, there needs to be an awareness that some products labelled as ‘fragrance-free’ may contain plant extracts which could trigger ACD in fragrance-sensitive individuals [2]. Kay Lin Ng: writing – original draft, conceptualization, methodology. Mei-Mui Tam: conceptualization, methodology, writing – review and editing. Rosemary Nixon: writing – review and editing. The patient has given their full consent for their information to be supplied. The authors declare no conflicts of interest.
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