Contact dermatitis to cooling lubricants is commonly encountered in occupational dermatology, but it rarely induces pigmentary skin changes. It is sometimes difficult to differentiate between toxic leukoderma and postinflammatory hypopigmentation when examining a depigmentation. A differential diagnosis is described in the case of a 31-year-old metal worker, spending most of his time on a computer-numerically controlled machine, who presented with cumulative irritant hand dermatitis and secondary hypopigmentation. Patch tests gave negative reactions to the European standard series, the desinfection and preservative series, the base preparation and emollient series, the metal series, the mechanical worker series as well as to the cooling lubricant itself. Atopy screening was positive for a variety of pollens. Based on biopsy findings, toxic leukoderma could be diagnosed even though none of the known melanotoxic compounds could be identified in his work environment. The patient was advised to avoid further contact with the regular composed cooling lubricant and the contact eczema improved dramatically, whereas the condition of hypopigmentation got better slowly within weeks under PUVA therapy.