The term medical device covers a wide spectrum of things and devices that come into contact with the bodies of patients and medical personnel. Materials from which the devices are made out of cause contact reactions in predisposed people. The reaction is immunologically mediated and corresponds to the type IV reaction by Coombs and Gell. The most common allergens are metal ions (nickel, cobalt, chromium), plastic materials (acrylates and epoxy resins) and natural latex. The reaction comes in an acute and chronic form. The signs of an acute reaction are pruritus, redness and vesicles. The signs of a chronic reaction are skin thickening and lichenification on the site of the skins contact with the device. The most common site of the reaction are hands which make up half of all incidences. In the case of presence of these signs and a founded clinical doubt an epicutaneous (patch) test is recommended. The epicutaneous test is the golden standard in diagnosing contact reactions. The test is conducted on the backs of patients and a standardized series of allergens are used. In the case of a positive reaction, the first course of treatment is avoiding contact with the source of allergen. For devices which are implanted within the body of the patient it means additional surgeries and stress for the organism. Depending on the severity of the clinical picture, a local or systematic therapy of corticosteroids is needed. Additional therapy of symptom mitigation by means of neutral creams or lotions and, if possible, introducing a barrier between the source of allergens and the body of the patient is recommended.