The pumpkin spice latte is back.

With temperatures dropping, nights closing in and Halloween around the corner, consumers are once more turning to the ever-present cinnamon, ginger and nutmeg-spiced drink for comfort.

But why are we so obsessed with the scent and smell of this autumn favourite?

According to scientists, it is all about our brains’ pleasure-seeking tendencies.

The parts of our brain involved in processing smells are close to, and have strong links with, the parts that deal with memories and emotions.

This means memories can be stored and retrieved easily when they are associated with a smell.

According to science journalist Alice Gray, from Cardiff, the scent of spices like cinnamon, nutmeg and ginger can therefore trigger happy, cosy and comforting memories.

Starbucks is credited with starting the trend for all things pumpkin spice.

According to the coffee chain’s website, the idea was born in a lab on the seventh floor of its HQ in Seattle.

Researchers brainstormed ideas for seasonal flavoured coffees and pumpkin scored high on “uniqueness”.

Its key ingredients are espresso, “pumpkin spice flavour sauce” and steamed milk, topped with whipped cream and a spice blend of cinnamon, ginger, nutmeg and cloves.

When the new pumpkin spice latte – known to its fans as the PSL – was tested with customers in 2003 it proved a hit.

But it was when consumers started sharing their love for the drink on social media that it went from a popular coffee flavour to a billion-dollar industry – featuring in candles, beer, lip balms and even dog treats.

Pumpkin spice ‘everything’ was born.

The global pumpkin spice products market was valued at $1.1bn (£823m) in 2003, and was expected to rise to $2.4bn (£1.7bn) by 2031, according to Future Market Insights.

The pumpkin spice latte is now a staple of coffee shops in the UK as well as the US.

When Chelsea Enness, 31, opened Scaredy Cats Cafe Bar in Cardiff two years ago, she quickly realised she would need to get it on to the menu.

“People were coming asking for it straight away, as soon as September started,” she said.

The café is currently getting through about six one-litre bottles of its homemade pumpkin spice syrup every week.

With a 25ml shot used in every drink, that is 240 pumpkin spice lattes.

And it goes far beyond coffee.

Vicky Isaac, 46, owns Little Bit Different, a wholesaler that supplies homemade candles to gift shops in Wales.

Her Latte Sbies Pwmpen candle – pumpkin spice latte in Welsh – was created in 2020 and is now one of her seasonal best-sellers.

As well as the usual spices, she adds vanilla, coffee and pumpkin to her candles.

She started making them in response to a joke she had seen on a US TV show about the popularity of the PSL.

She said: “We thought, let’s just have a laugh and see what happens. It didn’t matter if it didn’t work.

“But people really do love pumpkin spice. It’s a really good seller for us.”

She takes orders for her pumpkin spice candles from as early as August, so shops are stocked for September.

“The moment the weather changes, the children go back to school and the tourists all go home, it’s nice to have something different to make something of the season,” she added.

Science journalist Alice Gray said the smell rather than the taste of pumpkin spice products is key.

“The spices used in the pumpkin spice latte have strong associations with holiday seasons, and likely some comforting memories,” she said.

“So when you smell those spices, it will immediately activate emotive memories of joy, warmth and happiness.”

And if you’re sipping a pumpkin spice latte, the high levels of sugar in the drink also trigger the brain’s reward system, releasing feel good chemicals making us crave more.

But clever marketing also plays a part.

“The seasonal nature of a pumpkin spice latte hacks into the hunter-gatherer parts of our psychology,” said Alice.

“The fact that you can only get them in autumn gives them a sense of scarcity, which drives our desire to get our hands on them.”

Kiani Geldard, of Providero Coffehouse in Llandudno and Llandudno Junction, said that for many customers, pumpkin spice lattes are, “an accessible bit of joy”.

“It’s easy to attain and doesn’t cost the world to have that little moment of enjoyment with your PSL in the day, regardless of whatever else is going on,” she added.

In short, yes. But this is a hotly-debated topic.

Coffee enthusiasts argue that adding actual pumpkin is unnecessary.

Timothy Sharp, manager of Sparrow Coffee House in Cardiff, makes his own homemade syrup, adding spices like cloves, cardamom and star anise to the core PSL ingredients of ginger, cinnamon and nutmeg.

But pumpkin is not included.

“I see it as the spices that go into a pumpkin pie,” he said.

“I’m not sure I would want to taste pumpkin in my latte”.

However, Ms Enness insists actual pumpkin should be there.

Her staff order tins of pumpkin puree from the US, and add it into their syrup, which Chelsea said gives the coffee a distinct texture.

“I don’t think it changes the flavour that much,” she added.

“It’s just knowing that it’s in there.”