I remembered the book!

A brief history of vice, how bad behavior built civilization

By Robert Evans, very good book I highly recommend.

https://www.discovermagazine.com/the-sciences/ncbi-rofl-sexualization-of-the-female-foot-as-a-response-to-sexually-transmitted-epidemics-a-preliminary-study

There’s one article I found.

Originally read about it in a book that I don’t remember the title of.

Foot fetishes routinely come up more historically when there is a larger std concern.

People hear about diseased junk and become turned on about other things.

If you look through history, when there are large STD outbreaks afterwards foot fetish content rose.

Our brains are wired to be turned on by other things when the bits are diseased.