Image copyright BBC / Getty Images Image caption Rihanna, Justin Bieber and Shakira have all scored major summer hits

Summer is a magical time of year - the days stretching into one another as the tarmac steams and fruit ripens under a cloudless sky.

The warm-weather splendour also gives rise to a unique cultural phenomenon: The Summer Song.

Euphoric, frothy and fun - it's often as fleeting as the season itself, falling out of favour as soon as the leaves fall off the trees.

An early contender for this year's title seems to be Luis Fonsi's Despacito - a slinky, sensual slice of reggaeton ("despacito" means "slowly," referring to the speed of his seduction technique).

A worldwide hit earlier this year, it received a boost in the UK and the US after Justin Bieber jumped on the remix, singing an extra verse in a mixture of English and phonetically-learned Spanish.

But after eight weeks at number one, it could just be an extended drum-roll for the real song of the summer... whose identity we've yet to discover.

So what makes a summer smash? We've worked out six of the key ingredients below; while stars including Royal Blood, Dua Lipa and Clean Bandit nominated their song of the summer on this page.

1) It has to be simple

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The sun is out, school is out, and songs displaying any degree of emotional complexity are out.

Take, for example, Stardust's Music Sounds Better With You - four minutes of French funk built upon a brutally efficient four-bar loop, that became the signature sound of summer 1998.

Big, brash pop songs also fit the bill, with Rihanna's Umbrella (2007) and Little Mix's Black Magic (2015) both benefitting from a summer boost.

NB: This rule doesn't just apply to songs. Summer blockbusters are the dumbest form of cinema; "beach reads" are inevitably schlock romances and thrillers; and summer TV is epitomised by Big Brother and Love Island.

Basically, we all become idiots in the heat.

2) It should make you feel like you're on holiday

Image copyright Getty Images Image caption Los Del Rio: Heeeeeyyyyy Macarena

The rise of affordable package holidays in the 1980s prompted an influx of European songs to the summertime charts. Holiday hits like Spagna's Call Me, Sabrina's Boys and Opus's Live Is Life were all smuggled into the Top 40 by British tourists.

Ever since, summer songs have fared better if they somehow feel "exotic", with the rhythms of Latin America and the Caribbean providing several seasonal smashes.

Notable examples include Los Del Rio's Macarena (1996); Ricky Martin's Livin' La Vida Loca (1999); Rihanna's Pon De Replay (2005); Shakira's Hips Don't Lie (2006); OMI's Cheerleader (2015) and, of course, Despacito.

3) Novelty is everything

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The best pop music holds up a mirror up to society; and the best summer songs reflect a time of year when we collectively take leave of our senses.

How else do you explain Itsy Bitsy Teenie Weenie Yellow Polka Dot Bikini - an egregiously irritating song, both in its original 1960 guise and in Timmy Mallett's 1990 remix. Other offenders include Captain Sensible's Happy Talk (1982) and Whigfield's Saturday Night.

But novelty isn't always a dirty word. Songs with unique lyrics or arrangements often capture the carefree spirit of the summer.

Katy Perry scored her breakthrough hit with I Kissed A Girl in August 2008; while the whistled refrain of Maroon 5's Moves Like Jagger resurrected their career in summer 2011.

4) Radio-friendly songs make bigger hits

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If a single is going to float across the country and pollinate the population, it needs serious radio support. That means two things: 1) A catchy hook and 2) No swearing.

The song should also appeal to the widest possible audience, which often tips the scales in favour of grand emotional posturing and overblown sentiment.

Hence Bryan Adams' Everything I Do (I Do It For You) and Wet Wet Wet's Love Is All Around, which hogged the number one spot in summer 1991 and 1994 respectively.

In the modern era, though, summer hits have tended to be euphoric pop - with the likes of Carly Rae Jepsen's Call Me Maybe, The Black Eyed Peas' I Gotta Feeling and Sonique's Feels So Good all providing a soundtrack to the sunshine.

5) It should be released before the summer

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While it's possible for a late-breaking hit to elbow its way to the front of the pack, the song of the summer has usually been hanging around for a while before it takes over the world.

Drake's One Dance, which topped the charts for 15 weeks last year, was originally released in April.

More impressively, the reggae-tinged morality tale Rude, by Canadian band Magic!, had been hanging around for 11 months before it clawed its way to number one in August 2015.

6) But it should have the word "summer" in the title

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It's a cynical tactic, but it works.

From Mungo Jerry's lyrically-questionable In The Summertime in 1970 to Demi Lovato's Cool For The Summer in 2015, releasing a song about the summer in the summer guarantees you a hit almost as quickly as putting the words "featuring Justin Bieber" on the sleeve.

What are your songs of the summer? Drop us a line at entertainment.news@bbc.co.uk; and read what some of pop's biggest stars have chosen as their summertime smash on this page.