Which flavouring agent is most commonly implicated in plasma cell gingivitis and in oral lichenoid contact reactions?

Correct answer: C. Cinnamon (cinnamaldehyde)

• A. Menthol can cause a contact reaction occasionally, but cinnamon is by a wide margin the commonest culprit.
• B. Grape flavouring is not associated with plasma cell gingivitis.
• C. CORRECT. CINNAMALDEHYDE, the flavouring in cinnamon-flavoured chewing gum, toothpaste, mouthrinse and candy, is the classic cause of both PLASMA CELL GINGIVITIS (fiery-red, oedematous, sharply demarcated gingiva with a dense plasma-cell infiltrate on biopsy) and CINNAMON CONTACT STOMATITIS, which produces white keratotic and erythematous lichenoid patches on the buccal mucosa and lateral tongue. Removing the source resolves the lesion within one to two weeks — which is both the treatment and the diagnostic test.
• D. Citral in artificial lemon flavouring is a rare sensitiser and is not the classic association.

Note: Always ask about cinnamon products when you see a striking gingivitis or lichenoid lesion out of proportion to the plaque present. The lesions are often unilateral or asymmetric, corresponding to where the patient parks the gum or where the flavoured product pools.