Phototherapy: from ancient Egypt to the new millennium.

Phototherapy with ultraviolet light was widely and successfully used in the past for treatment of a variety of diseases. Phototherapy with visible light alone has no benefit except in the therapy and prophylaxis of unconjugated hyperbilirubinemia. For this purpose, radiation in the region of approximately 480 to 500 nm is most effective and radiation above approximately 550 nm is useless. The principle effect of the treatment is not photodegradation of bilirubin, but conversion of the pigment to structural isomers that are more polar and more readily excreted than the normal, more toxic "dark" form of the pigment. This, coupled with some photooxidation of bilirubin, diminishes the overall pool of bilirubin in the body and lowers plasma levels. In the future, phototherapy may be supplanted by pharmacologic treatment, but in the near future, the most likely advance will be the introduction of novel forms of light production and delivery.