As French photographer, Réhahn, was travelling through the South East Asian country, he observed that many people conceal their smile with their hand, as a mark of modesty or politeness.

He decided that the shy gesture would make an interesting subject for to focus on and travelled through the country snapping portrait photos for a series he called Hidden Smiles. 

Since giving up his hectic life in France, the photographer has spent three years in Hoi An, Vietnam, ranked the happiest country in the world, and says he has discovered their true meaning of happiness through his pictures.

In particular, Réhahn was keen to highlight how the smile is translated throughout every inch of the face, even when the mouth is covered.

Born in 1979 in Normandy, the photographer has enjoyed life travelling around Vietnam on his motorbike and has so far taken over 40,000 pictures. 

For Réhahn, a smile is more than mere muscle twitching and his Hidden Smiles project aims to celebrate the corners of the face etched by a lifetime of happy emotion.

'Vietnamese people are the most positive and optimistic people I've ever met in my life. It gives me a good energy everyday, just when I cross the small village where I live and meet many smiles. It's Feng Shui: only good energy!' he said. 

Looking past old age, or the wearing of poverty, the photographs reveal an energy and life behind the eyes of the individuals, through their concealed smiles. 

When asked why many subjects cover their mouths Rehahn said young girls do it out of embarrassment, and old women tend to do it out of elegance to cover their lack of teeth. 

'I think a good photography is when you can capture the soul, read a story in the eyes. Capture emotion is not an easy thing, Time is the key! Spending time with people always gave me better photos!' he said. 

Rehahn states he has only travelled to a quarter of the country, despite being a permanent resident there since 2011. 

Of the many photographs he has taken, 145 have made it to his first photo-book 'Vietnam – Mosaic of Contrasts,' which aims to show Vietnam in a natural and spontaneous light. 

The photographer has gained much recognition since publishing his book in January 2014. 

The 35-year-old has been featured in numerous newspapers and magazines, and has gained over 182,000 fans in one year on his facebook page. 

Rehahn is travelling to India in April to complete the collection and then will go to Mongolia in June.

His heart, however, lies in the happy nation of Vietnam. 

'Every month I am travelling in Vietnam by motorbike, to record the vanishing culture of ethnic minorities,' he said.  

(dailymail.co.uk)