Photodynamic diagnosis has proven to be a highly sensitive method to detect neoplastic tissues, whereas PpIX, although sensitive, has a high false-positive rate because it accumulates in benign conditions like scars and inflammatory tissues. Generally, normal skin surrounding lesions presents a weak fluorescence, varying with each patient and location. The contrast between this basal fluorescence and the pathologic fluorescence needs to be intense and sharp enough to obtain a good demarcation in PDD. Occasionally, in patients with severe actinic damage, actinic keratoses close to BCCs will also fluoresce under PDD, which could increase the excision area unnecessarily. Future methods for fluorescence quantification should reduce the rate of false-positive lesions. The varying depths of the tumors or their low cellularity might provide an explanation for the absence of fluorescence in false-negative cases.