Friday the 13th is considered to be the unluckiest day of the year by millions of people all over the world.

Triskaidekaphobia, the fear of the number 13, is a genuine medical condition.

Some airplanes also have no seat row numbered 13.

Airlines including Ryanair, Air France, Iberia, Continental Airlines and Lufthansa all skip the supposed unlucky number.

While the rate of people getting married on Friday 13th compared to other Fridays is lower.

But there might be some good news as well - it is claimed Friday the 13th is the cheapest day to fly, as superstition stops many people getting on a plane.

Origins of the myth

Several myths abound as to where the origin of the day actually came from.

One suggestion is that Jesus Christ was crucified on a Friday the 13th, another is that the Knights Templar - a medieval society - were arrested on Friday the 13th in 1307.

A belief popularised by Dan Brown's book The Da Vinci Code.

But according to National Geographic, it was not until 1907 that the day was associated with bad luck.

Graham Finlay is a lecturer at the School of Politics and International Relations at University College Dublin (UCD).

He told Newstalk Breakfast it depends where you are in the world that makes the day unlucky.

"In the Mayan religion 13 was unlucky, in Iran and in Persia 13 was unlucky...but it's a very powerful phobia".

"This was all consolidated by the 'Friday the 13th' movies which, if you look at them, don't have much to do with Friday the 13th".

"But they did a focus group test about the title 'Friday the 13th' to see if it would had a good reaction from a potential horror film base - and it did".

"And that seems to have consolidated fear of Friday the 13th".