Carvone (l-carvone), a mint flavour in spearmint oil, is considered a mild skin sensitizer. Carvone-sensitization may be linked to oral/perioral signs and oral lichen planus, but studies are sparse. The prevalence of patch test reactions to carvone and relevant findings from the positive group were investigated. Records for patch-tested patients at the Malmö clinic, for the period 1996 to 2016, were studied. Carvone-positive and carvone-negative patients were compared regarding patch test data from baseline series and dental series. Dental series-tested carvone-positive patients were also compared with a matched group. A total of 147 out of 4,221 referred patients had a positive patch test to carvone. Sensitized patients had higher mean age and were primarily women; 73% had oral signs and 57% had oral lichen. Concomitant patch test reactions to gold, nickel and mercury were common. In the matched group-comparison carvone-positive patients had a higher frequency of oral lichen, but no difference was found in sensitization to gold and mercury.

The majority of toothpastes on the Swedish market contain l-carvone, but the concentration hardly relates to the advertised flavour or labelled ingredients. It is hitherto unknown whether the found concentrations are sufficient for induction of contact allergy in individuals with healthy oral mucosa or in those with oral lichenoid lesions or other mucosal disease.

Background: Carvone (l-carvone) is a mint-tasting flavour additive that most of us is exposed to and can cause allergic contact reactions.Objectives: To analyse the frequency and the relevance of positive carvone reactions in a dermatitis population.Method: A retrospective analysis of dermatitis patients consecutively tested with carvone from 2017 to 2021. Data were retrieved from the department's patch-test database.Results: Of 3554 patients tested with carvone, 28 (0.79%) had a positive reaction.Carvone-positive patients had higher mean age, were significantly more likely female (p < 0.001) and had often an intraoral/lip involvement (p < 0.001). In the carvonepositive group, 50% (n = 14) had a relevant reaction, and in 4 of 14, the relevance was first revealed after test reading. Of the carvone-positive patients, 18 of 28 did not have a coexisting allergy to a fragrance/flavour allergen and of these 44% had a relevant allergy. Conclusions:The study suggests that a significant fraction of relevant carvone contact allergies may be overlooked if the allergen is not tested. Furthermore, as the exposure is widespread, inclusion of carvone in the Swedish baseline series may be justified even if the contact allergy prevalence is below 1%.

This thesis examines carvone (l-carvone), a mint flavour, and contact allergy to carvone with a focus on oral lichen. Carvone is a constituent of spearmint oil and is used to flavour toothpaste and food. Like many flavours and fragrances, carvone may cause contact allergy, but the prevalence is low, between 1.6 and 2.8%. Affected patients often have perioral or oral signs. A couple of studies have shown that patients with oral lichen planus or oral lichenoid lesions often have contact allergy to carvone but it is not known if these lichenoid lesions are a manifestation of contact allergy or part of the auto-immune disease, oral lichen planus. In paper I, the amount of carvone was measured in 66 toothpastes and the ingredient lists were studied. Carvone was detected in all toothpastes with flavour, even fruit flavoured toothpaste, in up to 0.35%. The measured concentrations were all within the safe use level estimated to not induce contact allergy, but carvone concentrations over 0.1% are high enough to elicit a reaction in already allergic individuals. The regulation of carvone as a constituent in toothpaste was discussed. Registry data (age, sex, referring information and patch tests results) on patients with a positive patch test reaction to carvone was studied in paper II. Data was retrieved from 1996 to 2016 and was compared with other patch tested groups not allergic to carvone. A matched comparison was also made between carvone-positive and carvone-negative patients tested with the same test series. Patients with contact allergy to carvone had a high mean age and were often women. According to the referrals, they often had oral signs and

Background: The mint flavour carvone (l-carvone) is considered a weak contact allergen. However, contact allergy to carvone is more prevalent in patients with oral lichen planus or oral lichenoid lesions (OLP/OLL).Objective: Our aim was to investigate how carvone affects sensitized individuals through a use test with toothpaste containing carvone. Non-flavoured toothpaste served as control.Methods: Subjects were patch tested prior to the use test-14 subjects allergic to carvone (11 with OLP/OLL), 20 subjects with OLP/OLL and 3 healthy controls. The month-long use test comprised of using toothpaste twice daily. Subjects were examined fortnightly. Clinical signs were assessed with a mucosal scoring system. The subjects' oral health-related quality of life was measured with the oral health impact profile (OHIP-49).Results: Local reactions to the carvone toothpaste presented as aggravated OLL (7/10) and peri-oral eczema (2/10) in allergic subjects. They also had significantly higher mucosal and OHIP scores compared with those receiving non-flavoured toothpaste. Conclusion:In sensitized individuals, oral exposure to carvone gives aggravated oral lesions and/or peri-oral eczema. The lesions mimic OLP and allergic individuals are therefore at risk of not being assessed with regard to flavour contact allergy.

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