Valentine’s Day, named after a Christian saint, may now be marked in countries around the world but traditions are often very different – and sometimes have nothing at all to do with romance.

While in Europe it is all about couples celebrating their relationship, in the United States it is as much about schoolchildren marking friendships, while in Japan women give chocolates to their bosses.

The origins of the annual February 14 occasion are shrouded in mystery but the day is, of course, associated with the cult of Roman Christian martyr Saint Valentine, who lived in the third century AD.

He literally lost his head over love – decapitated on the orders of Emperor Claudius II, they say, for secretly performing weddings. According to the legend, Valentine cured his jailer’s blind daughter and the day before his death slipped her a note signed “Your Valentine”.

In England, the exchange of messages known as “Valentines” on February 14 developed with the rise of the postal service in the 19th century, with the sender often signing off “Your Valentine”.

The celebration took a commercial turn in the mid-19th century in the US, with the invention of mass-produced greeting cards. Promoters quickly got the idea to extend the “tradition” beyond lovers, with schoolchildren often expected to bring a Valentine card for every one of their classmates.

Today it has become a $20bn business.

The Japanese Valentine tradition began after World War II when confectionery makers came up with the idea of having women offer chocolates to their bosses and boyfriends on February 14.

A half-century later, the practice has become an annual ritual, with millions of Japanese women giving pralines or ganaches to show affection, friendship or professional respect.

But elsewhere, the holiday – a relatively recent import from the West – often clashes with conservative cultural forces as well as anti-capitalist sentiment in parts of society.