A series of new stats about vaping show that e-cigarettes are getting more popular around the world.

Euromonitor International statistics, which have been published by the BBC, show that the number of vapers worldwide has increased rapidly, from seven million in 2011 to 35 million in 2016.

By 2021, the market research group forecasts that 55 million adults will vape across the globe.

This rapid increase comes as cigarette smoking rates decline.

The latest statistics from the World Health Organization (WHO) show a steady decrease in the number of smokers globally - falling from 1.14bn in 2000 to 1.1bn today.

WHO research shows the the fastest decrease in smoking rates has been in high-income countries. The proportion of smokers has actually increased in some lower income countries.

US spends $12bn+ on vaping

The research also showed that spending on e-cigarettes has increased exponentially, from $4.2bn five years ago to $22.6bn in 2016.

The United States, Japan and the UK are the biggest world markets for e-cigarettes. Vapers in these countries spent a combined $16.3bn on smokeless tobacco and vaping products in 2016.

The Untied States is the single biggest buyer of vaping products, with US vapers spending more than $12bn in 2016.

‘Open' systems the most popular

The Euromonitor International research split vaping products into ‘open systems’ and ‘closed systems’.

They found that open systems, a category which includes box mods with tanks, certain pen devices and refillable pod mods, are the most popular type of e-cigarette.

Non-refillable closed systems, like some cigalikes and pod mod devices, have gotten less popular relative to open systems.

Since 2011, the gap in spending on open and closed systems has gradually increased. This year, vapers are anticipated to spend two times more on open systems compared with closed systems.

Consumers want more choice

Separate research carried out by Ernest and Young surveyed vapers in the UK, France, Germany, Poland, Italy, Russia and South Korea.

The business analysts found that the e-liquid market is being driven by consumer demand for ever more extensive range of flavours and nicotine strengths.

In a snapshot of the market, they report that 16% of e-cigarette users choose nicotine-free e-liquid, 28% choose tobacco flavours, 23% choose fruity flavours and 20% choose botanicals.

Vapers think e-cigarettes are less harmful than regular cigarettes

When Ernest and Young asked vapers why they used e-cigarettes, the most common reason was that they are ‘less harmful than regular cigarettes’.

The second most common reason was that it helped users ‘reduce smoking factory made cigarettes’.

The research also found that an increasing number of vapers describe themselves as ex-smokers - up from 31% in 2013 to 37% in 2015.

There are more ‘occasional’ vapers

Ernest and Young research revealed that more vapers classify themselves as ‘occasional’ e-cigarette users as opposed to regular vapers.

Across the seven countries surveyed in 2015, just 38% of e-cigarette users said they were ‘regular’ users. This proportion has remained constant despite a growth in the e-cigarette market.

South Korea was the only country where more than half (58%) of e-cigarette users viewed their use as regular in 2015.