INTRODUCTION Carvone (l‐carvone), a mint‐tasting flavour often found in toothpaste, is considered a weak contact allergen and the prevalence of positive patch tests to carvone among dermatitis patients is 1.6–2.8%. However, contact allergy to carvone is more prevalent (12%) in patients with oral lichen planus (OLP) or oral lichenoid lesions (OLL) and patients with positive patch tests to carvone often have OLP/OLL. OLP is considered an autoimmune disease but the cause/relationship to carvone contact allergy is unclear. The aim of this study was to investigate how carvone affects the oral mucosa and peri‐oral area in sensitized individuals through a use test with toothpaste containing carvone. MATERIALS AND METHODS 16 allergic subjects with a positive patch test to carvone, 18 subjects with OLP/OLL only and 3 healthy controls were patch tested one week prior to the use test. Patch test preparations comprised test toothpaste, ± 1% carvone, and 10 different dilutions of carvone in acetone, 5%–0.000158%. During the month‐long use test, subjects were instructed to use 1 ml toothpaste twice daily and they were examined fortnightly. 5 allergic subjects received non‐flavoured toothpaste and all other subject received the same non‐flavoured toothpaste with 1% carvone added. Clinical signs were assessed with a mucosal scoring system by Escudier et al. and the subjects’ quality of life (QoL) were measured before and after the use test with a 49‐item questionnaire – oral health impact profile (OHIP‐49). RESULT Positive patch tests to carvone, ranging between ‘+’ and ‘++’, were recorded in 8 allergic subjects and 2 had late reactions (day 19 and 21). Five allergic subjects reacted to toothpaste with carvone. A majority of the allergic subjects had OLP/OLL at baseline (13/16). In four allergic subjects, the use test was terminated ahead of time due to mucosal/cutaneous lesions from carvone toothpaste. Allergic subjects reacted with aggravated OLL (7/10) and two displayed peri‐oral eczema. The mucosal score was significantly worse in allergic subjects receiving carvone toothpaste compared to those receiving non‐flavoured toothpaste. Additionally, allergic subjects with OLP/OLL had a worsening of mucosal score compared to subjects with OLP/OLL only. The difference of QoL, before and after the use test, showed the same pattern as the mucosal scores. CONCLUSION When exposed to carvone, allergic individuals may react with either aggravated OLL and/or peri‐oral eczema. These lichenoid lesions mimic OLP and therefore allergic individuals are at risk of not being investigated with regard to flavour contact allergy.