Recurrent allergic contact stomatitis and aphtosis, without cheilitis, due to stannous (tin)-containing toothpastes.

Dental consumer products are an important cause of allergic contact cheilitis,1 and stannous (tin) has been occasionally reported as a relevant culprit allergen in this regard.2-5 We here present a patient with a delayed diagnosis of allergic contact stomatitis with aphtosis, but without cheilitis, due to tin-containing toothpastes. A 23-year-old atopic female, known with psoriasis, suffered from recurrent episodes of oral stomatitis since >6 months. Each episode would start with itchy lips, without visible lesions, followed by the appearance of small itchy vesicles at the mucosal side of the lips and buccal mucosa, which subsequently broke down into small painful aphts, and sometimes localized hemorrhages, together with a sensation of swelling of the tongue and oral mucosa (Figure 1A). The lesions and associated complaints would usually lessen spontaneously after a few days, but resolution hardly ever occurred, and new and stronger attacks would occur every few days to weeks. The patient had received multiple tentative diagnoses (and associated treatments) including herpes simplex (acyclovir), angioedema (antihistamines, tranexamic acid), Behçet disease (colchicine), and burning mouth syndrome (clonazepam). She was eventually referred to our Dermatology department for further diagnostics and treatment advice. In the work-up of a (presumed) idiopathic recurrent oral aphtosis a mucosal biopsy only showed aspecific and discrete inflammation, a viral swab turned out negative, and blood analyses revealed no abnormalities. Because of the rather atypical complaint of associated pruritus, which also characterized the start of each new flare-up, she was patch tested to an extended baseline and cosmetic series (Chemotechnique Diagnostics, Vellinge, Sweden); personal products were not brought in at the initial test session. At the time, we had started to patch test various stannous (tin) salts as a supplement to our baseline series (tin 50% pet., tin chloride 1% pet. and tin oxalate 1% pet.; all from Chemotechnique). All preparations were mounted on AllergEAZE test chambers (Smartpractice, Calgary, Canada), occluded for 2 days, and read on D2, D4 and D7 per established guidelines. On D4 only positive reactions were observed to all three tin salts (all +, except to tin chloride ++; Figure 1B), and no later reactions occurred. Stannous fluoride was found to be present in two brands of tooth pastes, that is, Sensodyne (GSK, Brentford, UK) and Oral B (Procter & Gamble, Cincinatti, OH), the latter also containing stannous chloride (Figure 2), hence considered relevant for the recurrent oral stomatitis and aphtosis. Following the use of a sodium fluoride-containing toothpaste, the problem was completely resolved, with no recurrence after a follow-up time of 1 year. Seven cases of allergic contact cheilitis due to stannous (tin) salts in dental products have been reported so far in the scientific literature.2-5 In our previously published case3 also aphtosis was part of the clinical picture, yet in that patient associated to a clear cheilitis. In the present case the solitary mucosal involvement, without any concomitant cutaneous lesions, is remarkable, because often the reverse occurs, that is, cutaneous rather than mucosal involvement, as the latter is believed to exhibit a higher level of tolerance.6 Nevertheless, predominant or even solitary mucosal symptoms have also been attributed to other sensitizers (e.g., propolis, carvone).7, 8 Since the first observation in our centre (2018), we have documented other cases of contact allergy from stannous or tin in dental products (data on file), often involving patients with allergic contact cheilitis, yet some exhibiting more atypical symptoms (e.g., systemic allergic dermatitis with involvement of the large body folds, perianal itch).9 Although a discussion regarding optimal test modalities of stannous (tin) salts is beyond the scope of this short communication, our preliminary experience so far suggests that stannous chloride 1% pet. (too) often results in weak (1+) reactions, possibly reflecting false positivity, at least in some cases, whereas tin 50% pet. seems possibly more reliable (e.g., >1000 negative control tests), yet likely less sensitive as it produces occasionally only late weak positive reactions (e.g., 1+ only by D7). Tin oxalate 1% pet. might be a good in-between, also suggested by others,4 although this would need further confirmation. Also make-up (e.g., eyeshadow or blush) may contain tin salts (e.g., tin oxide).4 Notwithstanding that tin is considered a rare, weak and often occupational sensitizer, its presence and sensitizing potential in dental products and cosmetics might be underestimated. When confronted with patients suffering from (angular) cheilitis, stomatitis, and/or aphtosis, other cutaneous symptoms, or, as in the present case, isolated oral mucosal symptoms, especially when they use tin-containing products, we suggest to test these haptens to verify whether stannous (tin) might be a relevant culprit. Hannelore George: Writing – original draft; writing – review and editing; investigation. Ella Dendooven: Writing – original draft; writing – review and editing; investigation. Julie Leysen: Writing – original draft; writing – review and editing; investigation; project administration. Olivier Aerts: Conceptualization; investigation; writing – original draft; writing – review and editing; formal analysis; supervision. OA is investigator, consultant and/or speaker for Leo Pharma, Abbvie, Sanofi, L'Oréal/La Roche Posay and Bioderma/NAOS. JL is consultant and/or speaker for Sanofi, Leo Pharma, Lilly, Abbvie and Pfizer.