Mistletoe has often been a powerful component of many traditional faiths, believed to bestow life and fertility, offer protection against poison, or to create lustful thoughts. But its use as a Christmas decoration didn't take hold until sometime in the 18th century.

According to ancient Christmas custom, a man and a woman who meet under a hanging of mistletoe were obliged to kiss (relating to the plants relationship with sexuality). It was described in 1820 by American author Washington Irving in his The Sketch Book of Geoffrey Crayon:

"The mistletoe is still hung up in farm-houses and kitchens at Christmas, and the young men have the privilege of kissing the girls under it, plucking each time a berry from the bush. When the berries are all plucked the privilege ceases."

Interestingly, Mistletoe is actually quite toxic, especially the berries.  If ingested, symptoms may include gastrointestinal distress, stomach pain, a slowed heartbeat and other reactions.

Avoiding a kiss under the mistletoe brings bad luck (often in relation to one's love life). It is also bad luck to remove it from the house until it is replaced the next year.

Of course, not everyone you meet under the mistletoe is kissable! Click here for some tips on how to avoid the mandatory kiss!