The profession of a machinist includes various work tasks with the major aim of shaping raw metal pieces into products with well-determined measures, mainly by using semi- or fully automatic machine techniques. Main tasks of a machinist include setting up machines, turning, milling, drilling, and blowing off work pieces with compressed air. Mechanical and chemical irritation of hands and forearms often leads to irritant contact dermatitis and may increase the penetration of allergens into the skin and subsequent allergic contact dermatitis (ACD). Alkanolamines, especially monoethanolamine, preservatives like formaldehyde releasers and isothiazolinones, as well as colophony (resin acids), are major sensitizers in machinists handling water-based metal working fluids (MWF). Metals (in particular chromium) and epoxy resin are more often causative for ACD in metal workers without MWF exposure. Fragrances (odor masks) are usually not used in MWF anymore. Patch testing materials from patients’ workplaces is recommended, as not all allergens in MWF are available as commercial test preparations. Preventive measures include the use of skin protection and skin care creams. Infrequently, contact allergens in these products may also contribute to the occupational skin disease in machinists.