Cobalt is a frequent cause of contact allergy often seen with concomitant contact allergy to nickel or chromate, although solitary cobalt allergy is frequently observed. Cobalt allergy is prevalent among workers within hard metal, construction, and electronics industries and the healthcare sector. It is often difficult to evaluate the clinical relevance of patch test reactivity to cobalt for dermatologists, owing to scarce knowledge about sources of skin exposure. Cobalt has broad applications, especially within the areas of battery production and hard metal, alloy, and electronics industries. Cobalt is also frequently used as pigment in many different applications. It has been shown that cobalt-containing materials such as hard metals, alloys, and coatings have different abilities to release cobalt ions at skin contact and to cause allergic contact dermatitis. Quantification of cobalt on the skin by acid wipe sampling, identification of cobalt release from items and surfaces with a spot test, and the assessment of cobalt release from materials immersed in artificial sweat will increase the knowledge about sources of cobalt exposure and facilitate prevention of cobalt contact allergy.