Uncommon Source of Chromium Sensitization: Allergic Contact Dermatitis From Potassium Dichromate in Milk Adulteration Testing

Allergic contact dermatitis (ACD) from potassium dichromate is well recognised in India, mainly from cement and leather exposure [1, 2]. Its use as a laboratory reagent in milk adulteration testing, represents a potential but under-reported occupational hazard [3]. Milk adulteration refers to the deliberate addition of foreign substances or removal of natural constituents of milk to increase volume or falsely enhance quality. Detection is carried out using chemical reagents that identify adulterants such as starch, sugar, urea, detergents or oxidising agents. Potassium dichromate is used in certain laboratory-based milk adulteration testing protocols as an oxidising reagent and indicator. We describe a rare Indian case of ACD from handling milk samples treated with potassium dichromate. A 26- year- old female presented to the dermatology outpatient department with complaints of pruritic eczematous lesions present over both hands and forearms for the last 2 months. The lesions worsened during working hours and improved partially during weekends and holidays. On examination, there were eczematous plaques with erythema, scaling, fissures and crusts over the dorsum of the hands, interdigital spaces, and forearms (Figure 1A,B). There was no mucosal involvement, systemic symptoms, or history of atopy. Her occupational history revealed daily handling of chemicals used in milk adulteration testing, particularly potassium dichromate solution at a concentration of 10%, without adequate protective measures. She had been exposed for 4 months before the onset of lesions. Some of her coworkers were also affected, though their symptoms were minor and less prominent. Despite exposure to a relatively high concentration of potassium dichromate, the patient did not develop features of acute irritant contact dermatitis such as burning, erosions, or necrosis. Instead, the clinical presentation and temporal pattern were consistent with ACD, supported by the delayed onset of symptoms and strong patch test positivity. Patch testing was performed with the Indian Standard Series (ISS) (Systopic laboratories private limited, New Delhi, India), where potassium dichromate 0.5% in petrolatum elicited, a strong positive reaction (++ at 48 and 72 h), confirming the diagnosis of potassium dichromate–induced ACD (Figure 1C). Patch test readings and interpretation followed the European Society of Contact Dermatitis (ESCD) 2015 guidelines [4]. She was advised strict avoidance of potassium dichromate (Figure 2) exposure, substitution with alternative testing methods, and use of protective gloves. Topical corticosteroids and emollients were prescribed, leading to marked improvement within 3 weeks. Occupational ACD is the most common work-related dermatosis and remains an important cause of morbidity among exposed workers [5]. Chromium compounds, especially potassium dichromate, are well-known potent sensitizers and are most frequently reported in construction-related occupations such as cement handling, brickwork and leather processing [1, 2]. There are some reported cases of non-construction sources of chromium exposure such as laboratory reagent, photographic chemical, cooling tower water and industrial oxidising agents [3, 6]. However, reports of chromium-induced ACD in laboratory workers are rare, making the present case noteworthy. Potassium dichromate (K2Cr2O7) contains hexavalent chromium [Cr(VI)], which has high skin permeability and strong sensitising potential [7]. Cr(VI) readily penetrates the stratum corneum and is intracellularly reduced to trivalent chromium [Cr(III)], which then binds to epidermal proteins to form hapten–protein complexes that trigger a type IV delayed hypersensitivity reaction. In our patient, the temporal relationship with occupational exposure and the strong patch test positivity suggested that potassium dichromate served both as the sensitising and the eliciting allergen. Although the use of potassium dichromate in the milk adulteration testing has declined due to regulatory awareness, small-scale and rural dairy laboratories in India may still employ dichromate-containing solutions for adulteration testing because of cost-effectiveness and ease of availability [8]. Recent surveys indicate that while such exposure is uncommon, it persists in localised settings, highlighting the ongoing occupational risk. This case underscores the importance of recognising uncommon occupational sources of chromium exposure, including milk adulteration testing, in the evaluation of chronic hand dermatitis, as delayed diagnosis may lead to significant morbidity. Clinician awareness, workplace education, and early patch testing can improve prognosis. Manisha Balai: writing – review and editing, supervision. Asit Kumar Mittal: conceptualization, Supervision, Validation, Methodology. Arushi Sharma: resources, Supervision, Writing – original draft. The patient has given written consent for the publication of their clinical details and accompanying images. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.