Ultraviolet (UV) radiation has been used for decades with great success and at a constantly increasing rate in the management of
skin diseases, becoming an essential part of modern dermatologic
therapy (Krutmann et al, 1999). For
phototherapy, irradiation devices emitting either predominantly middlewave UV (UVB, 290-315 nm) or longwave UV (UVA, 315-400 nm) radiation are employed. In former years, patients were treated with broad-band UVB, broad-band UVA, or combination regimens. Broad-band UV
phototherapy, however, is being replaced more frequently by the use of irradiation devices that allow treatment of patients' skin with selected emission spectra. Two such modalities which have their origin in European Photodermatology are 311 nm UVB
phototherapy (which uses long-wave UVB radiation above 300 nm rather than broadband UVB) and high-dose UVA1
therapy (which selective employs long-wave UVA radiation above 340 nm). In Europe, 311 nm UVB
phototherapy has almost replaced classical broad-band UVB
phototherapy and has significantly improved therapeutic efficacy and safety of UVB
phototherapy (van Welden et al, 1988; Krutmann et al, 1999). The constantly increasing use of UVA-1
phototherapy has not only improved UVA
phototherapy for established indications such as
atopic dermatitis (Krutmann et al, 1992a, 1998; Krutmann, 1996), but has also provided dermatologists with the opportunity to successfully treat previously untractable
skin diseases, e.g.,
connective tissue diseases (Stege et al, 1997; Krutmann, 1997). These clinical developments have stimulated studies about the mechanisms by which UVB and UVA
phototherapy work. The knowledge obtained from this work is an indispensable prerequisite to make treatment decisions on a rationale rather than an empirical basis. Modern dermatologic
phototherapy has started to profit from this knowledge, and it is very likely that this development will continue and provide dermatologists with improved phototherapeutic modalities and regimens for established and new indications. This review aims to provide an overview about current concepts of the mode of action of dermatologic
phototherapy. Special emphasis will be given on studies that have identified previously unrecognized immunosuppressive/anti-inflammatory principles of UV
phototherapy.