A 56-year-old non-atopic female cleaner presented with a 3-year history of recurrent, pruritic eczematous eruptions affecting the right arm, upper back, posterior legs, and dorsal aspect of the right foot (Figure 1), which predominantly occurred during the spring and summer months. Given the pattern of her eruption, detailed history-taking revealed that the rash onset occurred within months after acquiring a new leather sofa, and the distribution corresponded to her seating position. She frequently rested her right elbow on the sofa armrest (Figure 1e) and typically wore sleeveless or short-sleeved tops and shorts during warmer seasons, allowing direct skin contact with the sofa surface. Allergic contact dermatitis (ACD) to the leather sofa was suspected. Neither the patient nor the distributor had applied any cleaning or preservation treatments to the sofa; however, the manufacturer confirmed the use of water-based coatings, including acrylic resins, pigments, and polyurethane resins. She was patch tested to the British Society of Cutaneous Allergy (BSCA) Baseline Series, additional series based on her history, and a sample of the sofa fabric. Readings were performed at day 2 and 4. Informed consent was obtained in written form. She had positive reactions to octylisothiazolinone (OIT) 0.1% in petrolatum (pet, 3+), potassium dichromate 0.5% pet (1+), shellac 20% in alcohol (1+), and to her sofa fabric (1+) (Figure 2). Patch testing was negative to dimethylfumarate (DMF) and 2-hydroxyethyl methacrylate (2-HEMA). The rash improved with mometasone ointment applied once daily to affected areas, emollients daily, and avoidance of direct contact with the sofa by covering this with layers of blankets. Sofa dermatitis typically affects the back, buttocks, dorsal thighs, and arms, sites in direct skin contact with the sofa. In 2008, an epidemic of sofa dermatitis surfaced due to DMF used as a fungicide in Chinese leather sofas 1; the EU has since banned the use of DMF in consumer products. Recently, sofa dermatitis has been reported due to OIT 2, 2-(thiocyanomethylthio)benzothiazole 3, cobalt 4 and leather-care products containing methylisothiazolinone (MI) 5. OIT is a preservative in non-cosmetic products, including cleaning agents, paints, glues, lacquers, and industrial chemicals. ACD due to OIT has been documented in leather products, including leather sofas 2 and leather car seats 6. OIT can demonstrate cross-reactivity with other isothiazolinones, including MI, increasing the potential for ACD in MI-sensitive individuals 7. Due to the increasing prevalence of ACD due to OIT, OIT has been added to the BSCA Baseline Series in 2022 7. Our patient may have been sensitised to this through her work as a cleaner and it is difficult to know if her eczema is partly occupational. Potassium dichromate is used in approximately 80%–90% of leather tanning 8, a process where raw animal skin and hides are converted into leather. For patients with chromium-induced ACD, vegetable-tanned leather is an alternative, using plant-based tannins such as oak, chestnut, or hemlock 9. Shellac, a natural resin secreted by the lac insect (Kerria lacca), is an alcohol-soluble substance widely utilised in dyeing, polishing, and finishing leather products. Due to its solubility in alcohol rather than water, shellac forms a durable, protective film upon application 10. To our knowledge, there are no previously reported cases of shellac-induced ACD associated with leather sofa dermatitis. Although the manufacturer confirmed the use of water-based coatings and pigments, the possible presence of shellac could not be excluded. Occupational exposure to shellac through polishing furniture remains a plausible source of sensitisation. The delayed onset of symptoms several months after acquiring the sofa is consistent with the immunopathogenesis of ACD, in which an initial period of sensitisation precedes the elicitation phase following repeated allergen exposure. In conclusion, sensitisation to OIT, potassium dichromate, and possibly shellac should be considered in cases of leather sofa-associated ACD. Awareness of these potential allergens and their presence in leather products is essential for accurate diagnosis and management of contact dermatitis in affected individuals. Jessica Hamilton: conceptualization, writing – original draft, methodology, visualization, writing – review and editing. Livia Francine Soriano: conceptualization, writing – review and editing, visualization, supervision. The authors declare no conflicts of interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
Hamilton et al. (Mon,) studied this question.