D1.39 - Oral Lichenoid Lesions Secondary to Contact Allergy to L-Carvone from Toothpaste: A Case Report

Background

L-Carvone is a cyclic monoterpene naturally present in spearmint and widely used as a flavouring agent in oral hygiene products. Although it is a well-recognised contact allergen, it is generally considered a weak sensitiser and is most commonly associated with mild allergic contact dermatitis. Oral involvement due to L-Carvone exposure is rarely reported and may be underdiagnosed in patients with chronic oral mucosal lesions.

Methods

We report the case of a 75-year-old woman with a previous history of hypersensitivity to iodinated contrast media who was referred from the Dermatology Department due to painful ulcerative lesions of the oral mucosa with a 3-year history of evolution. Histopathological examination showed findings consistent with a lichenoid reaction. The patient had undergone several cycles of systemic oral prednisone, achieving only transient improvement with subsequent recurrence of symptoms. She was receiving oral azathioprine at the time of assessment in our Allergy Unit. Patch testing was performed due to the suspicion of allergic contact involvement.

Results

Epicutaneous patch tests were carried out with the standard GEIDAC battery, as well as specific dental and acrylate series. Patch test readings at 48 and 96 hours showed a strong positive reaction (+++) to L-Carvone 5% with negative results for the remaining tested allergens. Based on these findings, a diagnosis of allergic contact oral lichenoid reaction secondary to L-Carvone exposure was established. Avoidance of mint-flavoured oral hygiene products was recommended.

Conclusion

This case highlights L-Carvone as a potential and probably under-recognised cause of chronic oral lichenoid lesions. In patients with persistent oral mucosal disease refractory to immunosuppressive treatment, allergic contact aetiology should be actively considered, and patch testing with dental-related allergens is essential. Identification and avoidance of the offending allergen may prevent unnecessary long-term systemic immunosuppression and significantly improve patient outcomes.