The history of photochemotherapy.

The combination of psoralens, obtained from plants, and sun exposure dates from antiquity. The main indication was vitiligo. In this century, extensive research on psoralens started in Egypt, where the active ingredients were isolated from plants and were soon thereafter commercialized for the treatment of vitiligo. The most important compound was 8-methoxypsoralen. When it was discovered that 8-methoxypsoralen inhibits the S phase of the cell cycle, it also started to be used in the treatment of psoriasis. In the meantime, the action spectrum was defined in the ultraviolet A (UVA) range (320-400 nm). Special UVA light boxes were constructed for total body irradiation. At first, the 8-methoxypsoralen was applied topically. Within a few years, high-intensity UVA bulbs became available, which permitted the 8-methoxypsoralen to be administered orally. Photochemotherapy or PUVA treatment as we know it today had begun.