They don’t.
Corns do not spread. They are not caused by an infectious agent (ie bacteria or virus) and are not contagious. You do not catch a corn from contact with another person (you can catch a verruca or warts from another person as its caused by a virus). If a corn develops in another place on the foot, it has not “spread”, that is a new corn that has been caused to develop in that new location for a reason.
The reason you get a corn in any one particular spot is because there is too much pressure in a small area (eg between a hammer toe and the shoe). Corns are caused by pressure. You can develop corns in multiple area if there is higher pressure in those area (eg from tight shoes). Just becasue the corns develop in several areas or places does not mean that they have “spread”. It means that you have multiple areas of higher pressure.
