The soft plant dangles in front of your face to set people up in a not-so-subtle way.
Yes, this tradition can be traced back beyond the middle ages. Now, these days fertility might be the last thing on your mind when you see a sprig of Mistletoe but that doesn't mean the greenery doesn't inspire some good old-fashioned smooching! Hey, there's nothing like smooching to get people into a holly jolly spirit! In so many ways, since you're the one wearing the seasonally colored head gear, you'll be the one puckering up the most. People saw that the vibrant plant stayed green throughout the winter and they thought, "Hey, bet that helps with fertility!".