A 26-year-old female, with a history of atopy, was referred for evaluation of cheilitis. Symptoms began in 2023 with oral tingling and sensitivity after using Oral B Toothpaste Sensitivity and Gum All Day Protection for 3 weeks. Despite cessation, she continued to experience intermittent episodes of cheilitis (Figure 1). Suspecting allergic contact cheilitis (ACC) she underwent comprehensive patch testing with the Australian Baseline Series, cosmetic common series, cheilitis and sunscreen common and rare series, toothpaste series and the patient's own products. Allergens were acquired from Chemotechnique Diagnostics. Patches were applied to the back using SmartPractice allergEAZE chambers 8 for 48 h, with readings at Days (D) 2 and 4. All D2 readings were negative. On D4 a strong positive reaction (++) to stannous chloride and an equivocal (+/−) reaction to tin oxalate was noted. Both were unable to be linked to any of the patient's current products. Weak positive reaction (1+) to methylchloroisothiazolinone and limonene occurred on D4 and was relevant as both were contained in the patient's shampoo (but not oral/dental products). This was ceased, and all allergens were judiciously avoided, but lip cheilitis persisted. Careful observation by the patient over 3 months identified a link between symptom exacerbation and the consumption of tinned foods (such as tomatoes and fish in brine), with flares typically emerging 1–2 days later. All tinned products were withdrawn, and treatment with tacrolimus 0.1% cream twice daily led to rapid resolution. Three months later, separate re-challenges to each tinned product were performed and symptoms reoccurred within 12 h. No further flares have occurred since ceasing tinned food consumption. Based on this, we suspect a diagnosis of ACC secondary to stannous salts with initial sensitisation from the patient's toothpaste, which was retrospectively noted to contain stannous chloride, and recurrent flares possible due to ingesting tinned foods that could contain trace amounts of stannous salts. Tin salts (Sn2+) rarely cause ACC, with exposure typically from stannous fluoride contained in toothpaste 1-3. Stannous chloride is also present in some toothpastes, such as that used by our patient; however, it is more commonly used in tin plating, a process to reduce corrosion of cans 4. Plastic and enamel coating can sometimes replace this 5. Dissolution of metallic tin from cans into food may occur, particularly in unlacquered or partially lacquered cans 6, or with acidic foods 4 (such as tomatoes) and result in the presence of stannous (Sn2+) salts in food 7. Other uses of stannous chloride include its role as a colour-retention agent and antioxidant 8. However, under Australia New Zealand Food Standards code, it is permitted only in asparagus up to 100 mg/kg 9. Manufacturers of the tinned foods consumed by this patient confirmed that stannous chloride was not present as a food additive but were unable to disclose packaging constituents. We therefore hypothesise that leeching of stannous salts into food could lead to trace levels capable of flaring ACC in highly sensitised patients. Positive patch testing results and recurrence of symptoms on re-challenge support this theory in our patient. However, the authors recognise the lack of confirmation from manufacturing companies makes this speculative. Previous reports of stannous contact allergies often show positive reactions to various tin containing compounds including stannous chloride, stannous fluoride, tin oxalate and sometimes elemental tin. This suggests potential cross-reactivity among stannous compounds, consistent with our patient's equivocal reaction to tin oxalate. Tin 50% pet was tested in our patient, and no reaction was observed at D2 or D4. Late weak positives for tin are common 3 but D7 readings were not performed. Stannous fluoride was also not tested. The absence of these represents a limitation in our study. This case raises the possibility that tinned goods could be a rare cause of ACC, highlighting that careful consideration of dietary sources of allergens should be warranted, particularly when typical exposures do not explain ongoing symptoms. Jessica McClatchy: writing – original draft, writing – review and editing. This research did not receive any funding in the public, commercial or not-for-profit sectors. Written informed patient consent has been obtained, including for the use of photographs which are de-identified where possible. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.
McClatchy et al. (Thu,) studied this question.