The application area recommended is the mid upper back skin, avoiding 3-5 cm on either side of the vertebrae. Apply the agents using e.g. the IQ Ultra Chamber technique. Apply duplicate sets on left and right side of the back of the patient and leave the test units in place for either 24 or 48 h, after which both sets are removed. At this point, one set should be covered with an ultraviolet (UV) opaque material and the other irradiated with a calibrated metered broad-spectrum UVA source. The type of lamp used for testing should be noted as this may affect results.