Two Cases of Facial Allergic Contact Dermatitis From Hexyl Resorcinol, a ‘New’ Resorcinol Derivative in Depigmenting Products

We report two cases of allergic contact dermatitis (ACD) from depigmenting skin care creams containing hexyl resorcinol (CAS 136-77-6). A 62-year-old non-atopic woman presented with a 3-month history of pruritic, well-defined erythematous macules and desquamation on the face and neck (Figure 1A). Patch tests were performed with the Belgian baseline, cosmetic and photo patch series, along with the patient's own products. Following an occlusion of 2 days, the tests were read on Day 2 (D2), D3 and D7 per established guidelines [1]. Only a positive reaction (++ on D3) was observed to Louis Widmer Pigmacare serum (Louis Widmer SA; Schlieren, Switzerland) (Figure 1B). Additional tests with the serums' ingredients, provided to us by the manufacturer, showed a positive patch test reaction to hexyl resorcinol 1% pet. (+ on D4). Two other resorcinol derivatives, that is, resorcinol 2% pet. and methyl resorcinol 1% pet., tested to verify any potential cross-reactivity, remained negative. A 21-year-old non-atopic woman developed a facial and neck eczema after using Avène Cleanance Tinted Emulsion SPF30 (Avène, Pierre Fabre; Castres, France), raising suspicion of ACD. Patch testing, performed as in Case 1, showed a strong positive reaction (+++) on D4 to this cosmetic, which had previously also resulted in a positive repeated open application test. Additional patch testing of the ingredients showed, also in this case, a positive reaction to hexyl resorcinol 1% pet. (++ on D4). Resorcinol 2% pet. and methyl resorcinol 1% pet., as well as phenylethyl resorcinol 0.3% eth/aq (50/50), remained negative. Resorcinol is a well-known yet rare true sensitizer in hair care products and topical medications [2-4]. Its derivative, resorcinol monobenzoate, can sometimes cause contact allergies to hearing aids or spectacles as it is used as a UV-light absorber in plastic materials [3, 5]. However, resorcinol derivatives have been increasingly highlighted as the cause of (severe) ACD because of their presence in skin-lightening products. Butyl resorcinol (2020) [6], phenylethyl resorcinol (2021) [7] and acetyl resorcinol (synonym: resacetophenone) (2023) [8] are some recent examples. The latter is occasionally also described as an allergen in anti-fungal topical medication [9]. Here we present the first two cases of ACD from hexyl resorcinol used as a depigmenting substance in skin care products. Moreover, in our cases, no cross-reactivity to resorcinol, methyl resorcinol, nor to phenylethyl resorcinol was observed, similar to other publications [6, 9, 10]. Although this may suggest the absence of cross-reactivity between resorcinol and its derivatives, and among these derivatives, it only concerns a limited number of patients, in whom resorcinol and its derivatives were often tested in different concentrations and vehicles, hence stressing the need for further research. Cille Van Echelpoel: conceptualization, writing – original draft, methodology, investigation. Silada Kanokrungsee: writing – review and editing, supervision. Olivier Aerts: supervision. Ella Dendooven: conceptualization, investigation, writing – original draft, supervision. The authors would like to acknowledge Louis Widmer SA (Schlieren, Switzerland) and Pierre Fabre/Avène (Pierre Fabre; Castres, France) for kindly providing samples of the individual ingredients. The patients gave permission to publish case details and photographs. O.A. is an investigator, consultant and/or speaker for Leo Pharma, Abbvie, Sanofi, L'Oréal/La Roche Posay and Bioderma/NAOS. The other authors declare no conflicts of interest.