Retrospective study of oral lichen planus and allergy to spearmint oil

Oral lichen planus (OLP) is a chronic inflammatory disorder with significant morbidity, associated with symptoms of pain and local discomfort. The concept of contact allergy aggravating or inducing OLP is recognised, and reported allergens include amalgam, metals used in dental restoration and flavourings. To date there has been only one case report of a contact allergy to spearmint oil in a patient with a 3-year history of OLP. We retrospectively reviewed our positive spearmint oil patch test data at the Skin and Cancer Foundation Victoria over a period of 11 years. In total 73 patients of the 1467 tested for allergy to spearmint oil had positive patch tests. The total number of patches tested during this time was 6134. Of the 73 positive reactions, 19 (26%) were classified as relevant, in that the patients had a history of using spearmint oil-containing products. Coexisting OLP and a spearmint allergy were found in 14 of these 19 patients. All patients had erosive OLP and were female. Patients, especially women, with OLP recalcitrant to treatment should be patch tested to flavourings, especially spearmint oil. We believe that spearmint allergy should be considered a cause of OLP, or at least, of oral lichenoid reactions.