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Persistent contact dermatitis following use of laurel oil

A 53-year-old patient presented to our clinic with severely itchy erythematous papules and vesicles on her knees and thighs that had existed for eleven days (Figure 1a, b). She reported that 14 days earlier she had applied bay oil to both knees due to knee pain. This oil was acquired in southern Europe. No details of the ingredients were found on the label of the bottle (only inscription: Laurel Oil). The patient was known to have hypertension, but she did not take any regular medication. There was no history of other allergies, atopic dermatitis, allergic rhinoconjunctivitis or bronchial asthma. Total IgE was increased by 400 kU/l (reference range <100 kU/l). Topical anti-inflammatory local therapy with class IV steroids was initiated with a suspected clinical diagnosis of allergic contact eczema. Despite this treatment, further lesions appeared in the areas of the trunk that were under pressure (Figure 1c), so that systemic prednisolone administration was initiated for five days, starting at 50 mg/d. After eight days the patient’s skin condition had improved and she was discharged. Gradual reduction of the prednisolone dose on an outpatient basis resulted in further deterioration of the findings. Complete healing of the skin changes was achieved after renewed topical steroid therapy over several weeks. Histology revealed an acute eczematous reaction with acanthosis and spongiosis of the epithelium, a marked subepithelial edema and a band-like lymphohistiocytic infiltrate with sporadic eosinophilic granulocytes and extravasated erythrocytes (Figure 2a, b). After healing, a patch test was carried out with the following series of tests from the German Contact Allergy Group (DKG): standard (DKG test series 1), topical preparations/excipients (18), preservatives (38), plant ingredients (15) as well as other fragrances and essential oils (44) in accordance with the recommendations of the current German S3 guideline [1, 2]. After 72 hours, there were three positive reactions to Compositae mix and sesquiterpene lactone mix, two positive reactions to parthenolide (feverfew) and ylang-ylang oil, as well as single positive reactions to Tanacetum vulgare (tansy) and lemongrass oil. However, bay leaf oil (from test series 44) was negative (Table 1, Figure 3a, b). The self-applied oil was not tested at the patient’s request, for fear of reactivating the eczema. Contact allergies to essential oils of laurel (Laurus nobilis) (leaves or seeds) are rare. The sesquiterpene lactone laurenobiolide is known to trigger a reaction to laurel. Many plants contain sesquiterpene lactones with antimicrobial, insecticidal and fungicidal properties that are useful in medicine or could be useful in future [3, 4]. Sesquiterpene lactones (e.g. custunolide) are strong contact allergens that can also trigger severe eczema. This can occur following contact with certain plants (especially Frullania; scale moss) and members of the Compositae (Asteraceae) family (e.g. lettuce, Clinical Letter