Multiple Allergens Causing Sofa Dermatitis: A Case Report of Polysensitisation

A 41-year-old female with a history of chronic plaque psoriasis treated with methotrexate, presented with well-demarcated, pruritic, erythematous, patches affecting her back and posterior thighs (Figure 1a). This predominantly affected the left side of her body with sparing of skin folds. She noted that the reaction corresponded to areas in contact with her new “Cozee 3-seater pure premium leather sofa” purchased 2 months ago, as she usually leaned against the left side of the sofa when sitting on it. Due to issues with mobility, the patient sat on the sofa most of the time. She was advised to avoid using the sofa and resolution was achieved with potent topical corticosteroid (mometasone furoate) applied for several weeks. A year later, she tried sitting on the sofa for just 30 min but developed a flare again. No further similar rash occurred subsequently by complete avoidance of contact with the sofa, although she continued to experience intermittent erythematous patches on her cheeks. Twenty-two months later, patch testing was performed (allergens from Chemotechnique Diagnostics, Villenge, Sweden on IQ Chamber, readings as per ESCD guidelines [1]) after holding methotrexate for a week. Testing was performed to allergens in an extended British baseline series, allergens reported as causative of sofa dermatitis and a small sample of the sofa. On day 4 review, there were multiple reactions (Table 1) including strong positive reaction to octylisothiazolinone (OIT) and to the sofa sample. Day 7 readings were not performed due to limitations on attending multiple appointments due to mobility, but photographs sent via email did not show any additional reactions to tested allergens. On further questioning, she had applied “Guardsman Leather Care Collection” on the first day of purchasing the sofa. These were listed as containing methylisothiazolinone (MI), methylchloroisothiazolinone (MCI), and 2-Bromo-2-Nitropropane-1,3-Diol (Bronopol) (Figure 1b). Interestingly, there was an unexpected positive reaction to Captan, an antifungal agent with no history of prior exposure to this. Mercapto mix and mercaptobenzothiazole (MBT) were also positive but not cobalt, chromate or dimethyl fumarate (DMF). We were unable to patch test for TCMTB as there is no commercially available preparation. As her facial personal care products contained fragrances including hydroperoxides of limonene, she was advised to discontinue use of fragranced products, resulting in resolution of the facial rash. Analysis by high performance liquid chromatography based on standard solutions showed the sofa sample only contained OIT. The sample was tested for MCI, MI, OIT, BIT, mercapto mix including MBT, TCMTB and Captan, following protocol detailed by Glas et al. [2]. Multiple allergens have been reported to be causative of sofa dermatitis, including cobalt, potassium dichromate, MI, MCI, OIT, DMF, and more recently, 2-(thiocyanomethylthio)benzothiazole (TCMTB) [3]. Historically, a large proportion of sofa dermatitis was caused by DMF, but in recent years, there has been a rise in cases caused by isothiazolinones, in particular OIT [4]. Isothiazolinones, including OIT and MI/MCI, are preservatives widely found in paint, polish, detergents, textile sprays, and leather products. Whilst 3a,4,7,7a-tetrahydrophthalimide (Captan) can be found in leather items [5], thus far, it has not been reported as causative of sofa dermatitis. Another allergen causative of sofa dermatitis, TCMTB, is not currently available as a commercial haptan for testing. Whilst concomitant positive reactions to both TCMTB, mercapto mix, and MBT have been reported [3], it remains unclear whether this is due to cross-reactivity or concomitant exposure. The sources of sensitisation to both Captan and MBT were not able to be identified in our patient. In this case, daily prolonged contact with the sofa due to decreased mobility and hyperhidrosis may have resulted in co-sensitisation to the allergens present. Alternatively, significant inflammation triggered by a single allergen could have led to subsequent sensitisation to other allergens in close contact with severely inflamed skin. In the diagnostic work-up of patients presenting with sofa dermatitis, it is important to consider allergens present not only in the furniture itself, but also additional products used by patients, as patients can be co-sensitised to allergens present in sofa-care products, such as in this case. We wish to highlight the multitude of allergens which need to be considered in sofa dermatitis, including checking for the use of furniture-care products. Bethany Neall: writing – original draft, writing – review and editing, investigation, project administration. Ying Xin Teo: supervision, writing – review and editing, conceptualization, project administration, resources. We thank Ola Bergendorff for assistance in the analysis of the sofa sample. I confirm that the patient gave consent for the pictures to be used in this case report. The authors declare no conflicts of interest.