Originally Posted by Stefan Blom

Direct formatting will usually be preserved as you continue typing, unless you are typing in a paragraph style which has a different style set as the "Style for following paragraph."

As I wrote, the easiest way to revert to the settings of the underlying paragraph style is by pressing Ctrl+SpaceBar, which runs the ResetChar built-in command in Word for Windows. If you are working mostly with direct formatting, you may lose other settings as well in the process. You should modify the document defaults to include the font characteristics you use most of the time.