If the thought of merely leaving the house this Friday the 13th has you spooked, you're not alone. The Stress Management Centre and Phobia Institute, based in Asheville, N.C., estimates that $800 million to $900 million US is lost every time the 13th of the month falls on a Friday, as people avoid doing business or flying.

The official names for fear of Friday the 13th are friggatriskaidekaphobia and paraskevidekatriaphobia. Sufferers can have symptoms as severe as panic attacks.

Stuart Vyse, professor of psychology at Connecticut College, said the superstition that associates Friday the 13th with bad luck is one of the most widespread in Western culture.

An article on the National Geographic website reports that between 17 million and 21 million people in the U.S. suffer from some degree of fear related to the day.

"It has a number of features that keep it alive," Vyse said. "If you grow up in the West, you can't avoid knowing it."

Part of what makes the superstition so pervasive is that having the 13th day of a month fall on a Friday now and then is unavoidable.

"You can go years without seeing a black cat or never walk under a ladder," Vyse said. "You can't avoid this one."

Despite the superstitions, the Insurance Bureau of Canada said there are no statistics showing an increased risk to drivers. In fact, it might be just the opposite.

"While we have no stats to support it … some insurers have said auto claims drop in some places, because so many people are afraid to leave their homes," said Steve Kee, director of media relations for the bureau in an email to CBCNews.ca

Origins

No one's exactly sure of the roots of the calendar-based fear, but there are several popular theories.

Some Christians tie together the belief that Judas — who would eventually betray Christ — was the 13th guest at the Last Supper, and Christ was supposedly crucified on a Friday. Other theologians have also theorized that Abel was slain by his brother Cain on Friday the 13th.

Jumping ahead to the 14th century, some believe the fear originated when King Philip IV of France had the Knights Templar arrested on Friday, Oct. 13, 1307. Looking to seize their vast wealth, Philip ordered the mass arrest of members of the Christian military order that had been active in the Crusades. Confessions for a variety of crimes, including heresy, were obtained from them with the help of torture.

This Templar theory has recently gained traction in pop culture as a result of references to it made in Dan Brown's novel The Da Vinci Code.

The number 13 is also considered unlucky in Norse mythology, with the mischievous god Loki being the uninvited 13th guest at a banquet of the gods. Loki would eventually trick the blind god Hoder into killing Balder, the god of joy and gladness, plunging the Earth into mourning and darkness.

Ancient Romans weren't huge fans of 13 either. They believed that witches gathered in groups of 12, and a 13th person joining them would be the devil.

But while there are references throughout history to both Friday and the number 13 being unlucky, there's evidence that the combination of the two is a creation of the 20th century. An 1898 edition of E. Cobham Brewer's Dictionary of Phrase and Fable, has entries for both the number and the day, noting both as unlucky but makes no mention of the combination of the two.

A 1907 novel by businessman Thomas Lawson, and simply titled Friday, the Thirteenth, tells the story of a stock broker trying to manipulate the market on Friday the 13th. It was fairly popular at the time it was published and may have helped to cement the idea of the day being unlucky.

Tempting fate?

For superstitious people, breaking a mirror is as likely to bring bad luck as Friday the 13th is. (iStock)

But not everyone fears Friday the 13th.

Motorcycle riders and fans descend on the town of Port Dover, Ont., every Friday the 13th for what has become a long-standing tradition. Beginning in 1981 with 25 friends meeting at a local hotel for drinks, the event now features beer tents, live music and merchandise. At the last gathering in May 2011, the radio station 680 News reported that the event drew more than 50,000 riders and spectators.

For those who aren't scared of going out on Friday the 13th and would rather scare themselves with a movie, the Viscera Film Festival in Vancouver can oblige. The festival, which is held at the Rio Theatre, features a series of short horror films from female directors. Tickets are, of course, $13.

Joe Nickell, a writer for Skeptical Inquirer magazine, likes to take it a step further and deliberately tempt fate when it comes to superstitions. Nickell has joined in several so-called superstition bashes held on a Friday the 13th. Participants follow an obstacle course that forces them to do things usually considered to cause bad luck, like stepping on cracks in the sidewalk.

'I've broken plenty of mirrors.'—Joe Nickell, writer, Skeptical Inquirer

"We would have tables set up where you can spill salt or break mirrors," he said. "I've broken plenty of mirrors."

The activities also move indoors to ensure all superstitions get a fair shake.

"We would open up umbrellas, and we have a large ladder that we set up so you have to walk under it," he said. "And as you can see, I'm still here."

Nickell said he thinks one of the big dangers with superstitions is that believing in smaller, more innocent superstitions can lead to believing in larger ones.

"Some people say things like, 'What harm will it do? It's just a rabbit's foot,'" he said. "Buying into one superstition will cause you to buy into larger superstitions.

"If you believe some mumbo jumbo will cure your cancer, that's a much bigger problem."