Allergic contact dermatitis caused by colophonium in resin creams

Colophonium (colophony, rosin, CAS no. 8050-09-7) is a common contact allergen: incidence of colophonium allergy in European patch tested patients during 2015–2018 was 3.11%.1 Among patients with suspected occupational contact dermatitis examined at the Finnish Institute of Occupational Health (FIOH) in 2002–2017, as many as 4.6% were patch test positive to colophonium.2 Exposure to colophonium can occur both at work and in private life. Common products used in domestic but also in occupational settings that contain colophonium include adhesive plasters and tapes, wound dressings, various types of cosmetics and timber.3-5 In Finland, over-the-counter resin creams seem to have gained popularity recently, especially for the treatment of small skin lesions. To find patients diagnosed with colophonium allergy and with a history of resin cream usage, we searched the patch test files from January 2018 to September 2022 to find patients with positive reactions (+/++/+++) to colophonium included in the baseline series. We reviewed their patient files to collect data on self-reported use of resin creams. At FIOH, all the patients are being examined for a suspected occupational disease. We perform patch testing with Finn Chambers (SmartPractice, Phoenix, Arizona) in accordance with the ESCD guidelines6 and read the tests 2 or 3 times (on day D2, D3 and D4; on D2, D3 and D6; or on D2 and D5), depending on the day of the week on which the patch tests were applied. Of the 479 patch tested patients, 26 were diagnosed with contact allergy to colophonium. Of them, 10 patients (38%) reported having previously used resin cream, and we considered six of them likely to have been sensitized to colophonium by resin cream use (Table 1). They all reacted positively to colophonium with either strong (++) or extreme (+++) positive reactions. Five of them had a positive reaction (++ or +++) to abietic acid and three had a doubtful reaction (?+) to it, while two were not tested with abietic acid (Table 1). Three of the 10 patients with a history of resin cream use were diagnosed with current (cases 4 and 9) or previous (case 7) occupational allergic contact dermatitis caused by colophony. Three patients (cases 7, 8 and 9) were considered previously sensitized to colophonium by exposure to oil colours, adhesive plaster, cardboard or pine wood dust that contained colophonium, and subsequently developed recurrence of allergic contact dermatitis while using resin cream. Patient 4 first developed eczema while using resin cream, and his eczema then recurred at work where he handled cellulose fibres that contained colophonium. Patient 10 was a nurse that had used resin cream for treating patients. Her colophonium allergy was considered possibly occupational, though of no current relevance. Seven of the patients had noticed their eczema was related to personal resin cream use. We did not record the trade names or other details of the resin cream products our patients had used, so the concentration of unmodified colophonium in the patients' resin creams is unknown. Colophonium from coniferous trees is a mixture of resin acids of abietane- or pimarane-type structures (90%) and neutral components (10%).3, 4 The abietic-type acid is the major resin acid and the main allergen in colophonium.4 Resin cream prepared from purified resin of Norway spruce (Picea abies) has been shown to have antimicrobial effects against bacteria (Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus species) and fungi (Trichophyton rubrum, tonsurans and mentagrophytes). Therefore, resin cream (a medical device that contains 10% Norway spruce resin) is used in professional wound care for chronic wounds.7, 8 Resin creams and other preparations typically with 5–30% spruce resin are also used for topical self-treatment of various skin conditions, for instance skin scratches, sores, sun burns, onychomycosis and paronychia.7 However, it is important to be aware of the potential sensitizing effect of the products. The risk of colophonium sensitization is likely to be even greater if the resin cream is applied to already damaged skin with impaired skin barrier as compared to healthy skin. Increased popularity of resin cream use might increase the prevalence of colophonium allergy, which is concerning. The current EU cosmetics regulation does not prohibit or restrict use of unmodified colophonium in cosmetic products.9 Our results call for a review of the regulation to ensure consumer safety. In our previous report on occupational contact allergy to colophonium, the majority the patients worked in the wood industry, in machinery, soldering or agriculture.2 It is noteworthy that in workers with occupational exposure to materials and substances that contain colophonium, sensitization to colophonium from resin cream use in private life may affect their ability to continue in their work. We found that even in the highly selected patient material of our clinic that consists of patients with suspected occupational contact dermatitis, as many as 38% of patients with colophonium contact allergy had a history of resin cream use, and in 23%, the resin cream was considered the probable source of sensitization. We conclude that usage of over-the-counter resin creams is a relevant source of colophonium sensitization. Susan Lievonen: Writing – original draft; investigation; writing – review and editing. Maria Pesonen: Conceptualization; methodology; data curation; investigation; formal analysis; writing – review and editing. Sari Suomela: Conceptualization; methodology; data curation; investigation; formal analysis; writing – review and editing; writing – original draft. MP: Speaker for UCB Pharma. SL and SS declare no conflicts of interest.