" Such planetary alignments are thought to lead to local miasmas: concentrations of fetid air and noxious vapors. These miasmas are then blown on the wind and enter men's and women's bodies through the pores of their skin. once inside they disrupt the balance of the 'humours" (the substances believed to control the body's functions), and people fall sick. "

― Ian Mortimer , The Time Traveller's Guide to Medieval England: A Handbook for Visitors to the Fourteenth Century