Photodynamic therapy is the general use of nontoxic light-sensitive compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells.
In the case of vitiligo, they work by increasing the sensitivity of melanocytes, the cells that manufacture skin color, to UVA light.
At least for vitiligo, narrowband ultraviolet B (UVB) nanometer phototherapy is now used more commonly than PUVA since it does not require the use of the psoralen and is easier to use with larger involved areas.
[citation needed] In Egypt around 2000 BC, the juice of Ammi majus was rubbed on patches of vitiligo after which patients were encouraged to lie in the sun.
[8] In the 13th century, vitiligo was treated with a tincture of honey and the powdered seeds of a plant called "aatrillal", which was abundant in the Nile Valley.
The plant has since been identified as A. majus,[9] which contains significant amounts of both bergapten and methoxsalen, two psoralen derivatives well known for their photosensitizing effects.
In the 1890s Niels Ryberg Finsen of Copenhagen developed a bulky phototherapy machine to treat skin diseases using UV light.
In 1900, the French electrical engineer Gustave Trouvé miniaturized Finsen's machine with a series of portable light radiators to heal skin diseases such as lupus and epithelioma.
[10] In the 1940s, Abdel Monem El Mofty from Cairo University Medical School used crystalline methoxsalen (8-methoxypsoralen, also called xanthotoxin) followed by sunlight exposure to treat vitiligo.