Henna has traditionally been considered safe as a natural dye for hair, skin and nails. However, recent reports of dermatitis are increasing. While often linked to para-phenyldiamine (PPD) additives, allergic reactions to pure henna are also emerging. This review aims to provide a focused clinical overview of allergic contact dermatitis (ACD) caused specifically by pure henna. We performed a systematic review of studies reporting on cases of ACD to pure henna. We searched PubMed, SCOPUS and Web of Science without time or language limits. Eligible studies required patch test-confirmed ACD to pure henna, excluding black henna, additives and reviews. Two reviewers independently screened titles, abstracts and full texts. Data on study details, patient characteristics, clinical features, patch testing techniques and treatments were extracted. Of 731 records, 13 met inclusion criteria for ACD to pure henna. Most cases involved women, though children were also affected. Reactions ranged from localised dermatitis to immediate hypersensitivity. Delayed forms were most common, occasionally bullous or pigmented. Patch testing remains the gold standard for delayed reactions, while prick testing aids in immediate hypersensitivity. Management mainly relies on avoidance. Corticosteroids, antihistamines and antibiotics were used in severe cases. Clinicians should remain aware of this uncommon but possible allergy.
Several cases of contact allergy to epoxy resins used in creative hobbies have been reported in recent years but not to "epoxy UV" resins. To determine which components present in "epoxy UV" resins were responsible for allergic contact dermatitis in three patients who used them to make jewellery as a creative hobby and to describe the clinical and chemical analytical work-up. The three patients with eczematous skin eruptions from "epoxy UV" resin were patch tested with a baseline series and epoxy series and/or additional (meth)acrylates, and in some cases with different benzophenones (patch tests and photo-patch tests). Proton Nuclear Magnetic Resonance (NMR) of three of the resins used was performed in order to determine their composition. All patients were shown to be sensitised to (meth)acrylates but not epoxy. Proton NMR could identify 2-hydroxyethyl methacrylate (2-HEMA) and an ethoxylated bisphenol A-based diacrylate oligomer in the three tested resins. For two resins, di(ethylene glycol) diacrylate and poly(propylene glycol) diacrylate were also detected. The resin of one patient could not be analysed because of a technical problem. Incorrectly labelled "epoxy UV" resins used in recreational activities are a new hidden source of sensitization to (meth)acrylates, not to epoxy compounds tested.
Photodynamic therapy (PDT) is an established treatment for actinic keratosis, with adverse effects usually limited to transient phototoxic reactions. Allergic contact dermatitis (ACD) to topical photosensitizers is rare and has mainly been reported in association with methyl aminolevulinate (MAL). Data on allergic reactions following laser-assisted PDT remain limited. A 67-year-old male patient with a history of previously well-tolerated laser-assisted PDT developed a severe eczematous skin reaction after laser-assisted PDT with 5-aminolevulinic acid (ALA) for the treatment of actinic keratoses of the scalp and arms. Patch testing after complete clinical healing revealed positive reactions to both ALA and MAL, while the vehicle and standard allergens remained negative, confirming the diagnosis of ACD to ALA. As only ALA had been applied clinically during the current and previous PDTs, the reaction to MAL was interpreted as cross-sensitization rather than evidence of clinical exposure. This case highlights ACD as a rare yet clinically relevant adverse effect of laser-assisted PDT and demonstrates cross-sensitization between ALA and MAL in the absence of prior clinical MAL exposure.
Allergic contact dermatitis (ACD) is a common and debilitating disease with a lifetime prevalence of 20%. Recently, the mast cell Mas-related G protein-coupled receptor B2 (MrgprB2) has been implicated in the pathogenesis of pruritus in ACD. Huanglian Ointment (HLO) demonstrates significant clinical efficacy in promoting skin healing, treating eczema, and alleviating skin inflammation and itching. However, the mechanism underlying the antipruritic effects of HLO has not yet been elucidated. This study aims to elucidate the potential mechanism underlying the therapeutic effect of HLO against ACD via the MrgprB2-mediated neuroimmune axis. In this study, scratching behavioral assays, transgenic mice (MrgprB2-/- mice), histopathological analysis, immunofluorescence, whole-cell patch-clamp technique, HPLC analysis, UHPLC-MS/MS, molecular docking and Bio-layer Interferometry (BLI) were employed to investigate the potential antipruritic mechanisms of HLO and berberine. Here, we demonstrated that HLO ameliorated pruritus in the oxazolone-induced ACD model by inhibiting mast cell activation and the subsequent release of tryptase, thereby reducing the abnormal excitability of dorsal root ganglion (DRG) neurons. In addition, knockout of MrgprB2 receptor could significantly reduce oxazoline-induced pruritus, tryptase release, and the abnormal excitability of DRG neurons. Notably, the therapeutic effect of HLO was significantly weakened in MrgprB2-/- mice, indicating that the mechanism underlying the antipruritic effect of HLO is potentially related to the MrgprB2-mediated neuroimmune axis. Furthermore, component analysis of HLO combined with molecular docking screening suggested that berberine could serve as one of the potential key bioactive components. BLI assays implied a relatively preferable binding interaction between berberine and MrgprX2 protein. Further data also indicated that berberine might mitigate pruritus in ACD model, and such anti-pruritic activity is presumably correlated with the MrgprB2 receptor. In conclusion, our findings indicated that HLO could effectively alleviate pruritus, and this effect may be linked to the MrgprB2-related neuroimmune axis. Berberine may potentially act as an active component involved in HLO's antipruritic pharmacological effects.
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Few recent studies have examined differences in patch test results between racial/ethnic groups. To analyze patch test results by race/ethnicity in the US and Canada. Retrospective cross-sectional analysis of 32,138 patch-tested patients, comparing results between White (non-Hispanic), Black, Asian, and Hispanic patients. Most patients were White (86.5%) followed by Asian (6.8%), Black (4.8%), and Hispanic (2.0%). Thirteen of 50 allergens differed significantly across groups (all p<0.001): nickel, cobalt, neomycin, p-phenylenediamine (PPD), disperse dyes, balsam of Peru, fragrance mix II, formaldehyde, quaternium-15, lanolin, propylene glycol, thiuram mix, and colophony. White patients had the highest proportion of positive patch test reactions to balsam of Peru, neomycin, quaternium-15, and fragrance mix II; Black patients had the highest proportion of reactions to PPD and disperse dyes; Asian patients had the highest proportion of reactions to nickel, cobalt, and thiuram mix; and Hispanic patients had the highest proportion of reactions to propylene glycol (all p<0.001). Tertiary referral population with disproportionate representation by racial/ethnic groups. Race/ethnicity are social constructs. Patch test results differ across racial/ethnic groups, which may relate to sociocultural variations in allergen exposures. These findings can facilitate allergen identification and avoidance in diverse populations.
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Atopic dermatitis (AD) and allergic contact dermatitis (ACD) are common inflammatory skin diseases in both children and adults that present similarly and often coexist. Patch testing is the gold standard for establishing the diagnosis of ACD and can often help distinct between the 2 conditions. Patch testing is more challenging in patients with underlying AD due to potential for angry back reactions. In this review, we discuss the current evidence and guidelines regarding the screening for contact allergies in patients with AD. We also discuss the most frequent relevant allergens in adults and children with atopic dermatitis.
Allergic contact dermatitis (ACD) and atopic dermatitis (AD) are driven by distinct T cell programs, and safe long-term topical therapies remain limited. Dermal fibroblasts (dFBs) have emerged as active immunomodulators, but whether they can be therapeutically targeted remains unexplored. Here we developed MDI1228, a novel topical pan‑JAK inhibitor with nanomolar potency against JAK1/2/3/TYK2 (IC₅₀ 0.11-0.85 nM) and high selectivity. MDI1228 was evaluated in DNFB‑induced ACD and MC903‑induced AD mouse models, as well as in primary mouse and human cell‑based assays. Topical MDI1228 ameliorated both ACD and AD in mice, reducing T cell infiltration and cytokine production. Mechanistically, MDI1228 not only directly inhibited T cell activation and cytokine production but also disrupted fibroblast‑T cell crosstalk by reducing dFB‑derived chemokine expression. Single‑cell transcriptomics identified dFBs as the primary source of CXCL9/10 in ACD and CCL2 in AD. Conditioned medium and neutralization experiments demonstrated that CXCL9/10‑CXCR3 and CCL2‑CCR2 signaling axes contribute to T cell polarization in a context‑dependent manner. Compared with glucocorticoids, prolonged topical application of MDI1228 showed minimal systemic toxicity and preserved tissue homeostasis. These findings identify dFBs as a central therapeutic node and demonstrate that MDI1228, by directly targeting T cells and disrupting dFB‑derived chemokine axes via JAK inhibition, offers a potent and safe topical treatment for both ACD and AD.
This is Part 1 of a 2-part narrative review of contact allergy and allergic contact dermatitis (ACD) to alkyl glucosides. It discusses the nature of alkyl glucosides (mainly decyl, lauryl, cetearyl, and coco-glucoside), their properties and applications, results of patch testing in routine testing and in groups of selected patients, and presents all reported case series and case reports of ACD to decyl and lauryl glucoside. The alkyl glucosides are nonionic surfactants that are produced by the reaction of glucose with fatty alcohols and that are increasingly being used in cosmetics. This class of surfactants and emulsifiers has a low potential for irritation and favorable ecological characteristics, being manufactured from renewable sources and being completely biodegradable. Alkyl glucosides are chemically stable and hardly protein-reactive; they do not contain chemically reactive sites or strongly polarized structures. Therefore, they were not predicted to have allergenic potential. Yet, they can induce contact sensitization, which is increasingly recognized. Currently, decyl glucoside has a rate of 2.4% positive reactions in routine testing in the United States. Most positive patch test reactions have current relevance, in >80% from their presence in personal care products. Part 2 will discuss patient demographics (gender and age, atopic diathesis, distribution of dermatitis, occupational contact dermatitis), products causing ACD, patch test considerations, co-/cross-reactions between alkyl glucosides and nonrelated haptens, and the presence of alkyl glucosides in cosmetics and other products.