Psoriasis is a skin disease, normally characterized by scaly, reddish, and itchy patches. The word was borrowed in 1680 from medical Latin, which comes from Ancient Greek psoriasis. This was less specific to a certain kind of condition, and just referred to having itchy skin in general. Psoriasis comes from the word psorian, meaning "to have the itch", which comes from psora, a word with the plain ol' definition of "itch" (once we eliminate the -sis suffix indicating a noun of action, that is). This could also be used to individually refer to scabies or mange, but the broader denotation still stood. Because you rub your itches, this hails from psen, meaning "to rub", and that comes from a Proto-Indo-European root with the same definition. Usage of the word psoriasis peaked in the 1870s but is now enjoying a healthy comeback. Google searches for it have also increased, as more and more people seem to be suffering from it.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
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