The present invention relates to a composition comprising a photosensitizer use in prevention or treatment of dermatological disease in a patient, wherein the composition is used in the following order of steps:

(a) topical application or subcutaneous injection of said composition to an area of the skin of said patient,
(b) exposure of at least said area of the skin to light with a wavelength spectrum similar or identical to sun light for a duration of 30 min to 5 hours, and
(c) exposure of at least said area of the skin to light of a wavelength spectrum comprising only one maximum in the absorbance spectrum of said photosensitizer

as well as to methods of treating dermatological disease using the outlined steps and kits of parts comprising such compositions and light sources suitable to apply the respectively indicated light.