A Fish‐Farmer With Occupational Allergic Contact Dermatitis From Octylisothiazolinone in Polyurethane Boots

Octylisothiazolinone (OIT) is a biocide agent widely used due to its antifungal and antibacterial properties. It can be found in different products such as paints, detergents, cutting fluid, textiles, and the leather industry [1] and it is known to be responsible for allergic contact dermatitis. A 55-year-old male without a history of atopy, diagnosed with chronic venous insufficiency, was referred by the Dermatology Department at San Pedro Hospital Logroño due to a one-year history of an eczematous eruption on the lower limbs. Initially, the patient exhibited isolated erythematous-squamous plaques, leading to a diagnosis of infected eczema, for which he received treatment with oral antibiotics and topical corticosteroids. Despite this intervention, there was no improvement. Over time, the condition progressed, with the eruption worsening and spreading to involve the ankles, pretibial regions, and dorsal arches of the feet, culminating in the development of exudative and ulcerative lesions (Figure 1). The patient worked in a fish farm, where he routinely wore polyurethane boots with socks. He did not develop any lesions on his hands upon contact with fish and reported no adverse reactions to fish consumption. Prick testing was conducted using a mix of white and blue fish extracts (Probelte Pharma), latex (Roxall), and prick-by-prick testing with cod, tuna, and trout, all of which yielded negative results. Patch testing was performed under occlusion for 48 h, using the Spanish Contact Dermatitis and Skin Allergy Research Group (GEIDAC) baseline series, supplemented with benzisothiazolinone (BIT) and series for rubber additives (Martí Tor, Barcelona, Spain), textile dyes, plastics and glues (Chemotechnique, Vellinge, Sweden). Additionally, a 5 × 5 mm moistened sample from the interior and exterior surfaces of the patient's boot was tested using Finn Chambers (SmartPractice, Phoenix, AZ). Patch testing revealed a strong positive result (++) on day (D) 2 and (++) D4 to OIT 0.1% in petrolatum (Lot. n° 21414A-6a), as well as to both the interior and exterior surfaces of the boot. All other tested substances, including other isothiazolinones such as methylisothiazolinone (MI), methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), and BIT, produced negative results (Figure 2). As the technical sheet for the boots did not disclose the materials used in their manufacturing, a sample was sent for chemical analysis to the Instrumental Analysis Service of the Institute of Grapevine and Wine Science (ICVV). The analysis aimed to detect the presence of OIT was studied by liquid chromatography coupled to mass spectrometry. To prepare the sample, an extract was obtained from the boot material by adding methanol. The concentration of OIT in the boot tissue was determined by extrapolation from a calibration curve obtained for standard OIT solutions of varying concentrations. The analysis was conducted using a Shimadzu Nexera Ultra High-Performance Liquid Chromatograph (Shimadzu Corporation, Japan) coupled to a Sciex 3200QTRAP mass spectrometer (Sciex, USA). A peak detected at 4.1 min corresponded to the compound OIT (Figure 3). The identification and quantification of OIT in boot material based on this peak, revealed a concentration of 194 μg OIT per gram. Octylisothiazolinone is a member of the isothiazolinone group of antimicrobial compounds. While legislation exist for other isothiazolinones, such as MI and MCI/MI, concerning maximum allowable concentrations in cosmetics and industrial products, OIT and BIT are prohibited in cosmetics within the European Union. However, there are no regulations governing their use in other products [1, 2]. This regulatory gap, combined with the widespread use of OIT, may contribute to an increase in cases of contact dermatitis. Although contact dermatitis caused by OIT in polyurethane products is rare, at least one other case has been reported in the literature [3]. Russo et al. [4] described cross-reactivity to OIT in patients primarily sensitised to MI. However, in this case, the patient, who was primarily sensitised to OIT, did not exhibit cross-reactivity to other isothiazolinones. We present a case of occupational allergic contact dermatitis caused by OIT in polyurethane boots. The patient's chronic venous insufficiency, which compromises the integrity of the skin barrier, likely played a significant role in facilitating sensitization. Based on the confirmed presence of OIT in the boots and the complete resolution of eczema following discontinuation of their use, we conclude that OIT was the causative agent of the patient's dermatitis. Diana Alejandra D'Elia Torrence: conceptualization, investigation, writing – original draft, writing – review and editing, project administration. Mónica Venturini Diaz: conceptualization, investigation, writing – original draft, methodology, validation, writing – review and editing, project administration, supervision. Irene Vidal Orive: conceptualization, investigation, writing – original draft, validation, writing – review and editing, supervision. Miguel Ángel Fernández Recio: conceptualization, investigation, writing – original draft, methodology, writing – review and editing, formal analysis. Elizabeth Landeta-Iza: investigation, writing – original draft. Ángel Blasco Sarramián: conceptualization, writing – original draft, writing – review and editing. The patient signed an informed written consent. The authors declare no conflicts of interest. Data sharing for immunological testing, as well as the detailed methodological and chromatographic data from the chemical analysis, will be available upon request to the authors.