Photosensitizers have been used in medicine for several thousand years. In the past, the effect being sought was repigmentation of light areas in the skin. Most of the orally administered or locally applied preparations were obtained from plants that contain psoralen (furocoumarin).1 Only with the work of Kuske2 and that of Fahmy and Abu-Shady3 did scientific investigation of these compounds begin. Since then scientific and clinical investigations have continued in many countries.
Pathak and co-workers4,5 studied the relationship between the molecular configuration of furocoumarins and their ability to photosensitize to long-wave ultraviolet light. The most active compounds were found to be psoralen, 4-methylpsoralen, 5′-8-dimethylpsoralen, 4-5′-8-trimethylpsoralen, 8-methoxypsoralen, and 5-methoxypsoralen. Further investigation6 of the excitation fluorescence and phosphorescence wave-lengths of psoralen indicated the probable sequence of change. Ultraviolet light in the range of 360 mμ induces the formation of free radicals in the psoralen molecule, and this
Becker SW. Psoralen Phototherapeutic Agents. JAMA. 1967;202(5):422–424. doi:10.1001/jama.1967.03130180088019
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