Since the skin is a large organ, exposure of circulating immune cells to UVA-1 irradiation through the cutaneous vasculature may allow considerable systemic ramifications. Much of the early work in this realm has been done in Europe, where efficient sources of UVA-1 radiation are more widely available.
Ultraviolet radiation is a well-known modulator of immune responses in the skin.
Although extensive work has been done to investigate the effects of UVB and PUVA on the skin's immune system, little is known about the photoimmunological effects of UVA-1 irradiation. Eosinophils are known to be of pathogenic importance in atopic eczema. UVA-1 has been widely reported. The beneficial responses of morphea and scleroderma have been substantiated with ultrasound assessment and cutaneous elastometry. High doses of UVA-1 require a special light source that allows manageable treatment times.