Photodynamic therapy provides the possibility to find specific pathologically altered cells and to destroy these without adverse effects through an exposure to light. It is suitable for treatment of superficial tumors and certain forms of skin cancer. Pretreatment with a so-called “photosensitizer” occurs during this therapy. This is a photosensitive dye which is applied to the affected skin areas by means of cream and which then accumulates in the damaged tissue. This procedure particularly leads to a very good cosmetic result.