Contact allergy to 2,5-dimercapto-1,3,4-thiadiazole and phenyl-alpha-naphtylamine, allergens in industrial greases and lubricant oils--contact allergy to water-insoluble greases is uncommon but needs to be considered in some workers.

Industrial lubricants are usually made of petroleum and contain no water. Industrial greases and neat oils (insoluble metalworking oils) cause contact allergy relatively seldom, and reported allergies to the components of engine oils, such as hydraulic oils, are extremely scarce. The aim was to describe patients with contact allergy to the components of industrial lubricants. We describe 2 patients with allergic reactions to 2,5-dimercapto-1,3,4-thiadiazole. Their allergies derived from guide-way oil and grease. Guide-way oils are lubricants for metalworking machines. Machinists may have continuous skin contact to these oils, as the oils are leaked to the circulating metalworking fluid system and form the so-called 'tramp oil'. We also report a new case with allergy to phenyl-alpha-naphtylamine in grease. 2,5-Dimercapto-1,3,4-thiadiazole is an aromatic compound used in oils and greases. It has previously caused contact allergy to workers who have handled the pure chemical, but to our knowledge, there are no previous reports of contact allergy from products containing the chemical in a relatively low concentration. 1 of our 2 cases had been sensitized from grease and the other from a guide-way oil. The latter case shows that machinists may become sensitized to lubricants that leak to the metalworking fluid system.