Tess Christian's female friends look the picture of merriment when they get together for their frequent Friday nights out in a local restaurant.

Champagne flows, the conversation gets steadily more raucous and peals of laughter hang over their table.

But there’s always an odd one out in the happy scene: Tess, 50, who sits stony-faced while her friends giggle around her. Not even a flicker of a smile, let alone a laugh, escapes her lips.

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Tess Christian, 50, (pictured) does not allow a flicker of a smile to pass her lips, and hasn't for almost 40 years, in an attempt to ward off wrinkles

Tess isn’t devoid of humour, but for nearly 40 years she has made a conscious decision not to laugh or smile — even at the birth of her daughter. This is because Tess says that maintaining a perennial poker face is a crucial way to keeping her — admittedly, impressive — youthful looks.

‘I don’t have wrinkles because I have trained myself to control my facial muscles,’ says Tess, ‘Everyone asks if I’ve had Botox, but I haven’t, and I know that it’s thanks to the fact I haven’t laughed or smiled since I was a teenager. My dedication has paid off, I don’t have a single line on my face.

‘Yes, I am vain and want to remain youthful. My strategy is more natural than Botox and more effective than any expensive beauty cream or facial.’

Tess (right) is pictured here with Jane Vintner (left) in 1982, aged 19. Tess says she has trained herself to control her facial muscles

As unorthodox as Tess’s regime may sound, she is not alone in her drive to suppress facial movements, such as laughing or frowning, in a bid to stop wrinkles forming.

Even celebrities such as U.S. TV star Kim Kardashian, 34, have admitted trying not to smile or laugh ‘because it causes wrinkles’.

And some experts believe that this bizarre trick might work. Dermatologist Dr Nick Lowe says: ‘It can be an effective anti-ageing technique. Undoubtedly, there are some actresses who have retrained their facial expressions to this end.

Tess, pictured here in 2001, aged 36, admits she is vain because she wants to remain youthful but says her strategy is 'more natural than Botox and more effective than any expensive beauty cream or facial’

‘Wrinkles happen because of the constant creasing of smile and forehead lines by the muscles in your face, which fold the connective tissue under the skin. If you can train yourself to minimise your facial expressions, you won’t get as many lines.

‘We know this because it is exactly how Botox works — by reducing muscle activity. Not smiling is a DIY option, although I would have thought it difficult to keep up, not to mention boring for your partner and confusing for your children.’

So, is a life full of laughter really worth sacrificing for the sake of a few lines? Tess, who works as a cooking instructor for a vegetable produce company, thinks so. ‘It’s not as if I’m miserable. I love life. I just don’t feel the need to show it by walking around with a rictus grin on my face.’

Tess, 43, (left) pictured with her daughter Stevie, 16, (right). Tess says she has learned to control her facial muscles to stop herself from smiling

Her decision didn’t start off as an anti-ageing device. Instead, it was a reaction to the strict Catholic school she attended.

‘The joyless nuns there didn’t like children to smile. I was always told to wipe the smile off my face so I learnt to smirk instead,’ says Tess.

By the time she reached adulthood, she realised a sombre expression suited her. ‘If I did smile I developed big hamster cheeks that made me look deranged. I looked up to old-school Hollywood icons such as Marlene Dietrich for inspiration; she never smiled and I loved the way she smouldered glamorously.’

Tess, (left) aged 23 yrs, in 1985. Tess says although she was overjoyed when her daughter was born and when she got married, she kept a straight face the whole time

Staying tight-lipped required effort at first, however. ‘When I found something funny or I was tempted to laugh — which happened on a daily basis — I learned to control my facial muscles by holding them rigid,’ explains Tess.

‘The corners of my mouth might go up a little, but I never looked anything other than faintly amused. Friends knew I was fun to be around, so it wasn’t an issue.’

She met her ex-husband Nigel, now 54, a photographer, at a bar in 1990 and they had a daughter, Stevie, in March 1991. ‘Nigel was never bothered about me not smiling, because I kept him entertained — I am engaging company. If you spent a day in my presence you wouldn’t even notice.

The joyless nuns there didn’t like children to smile. I was always told to wipe the smile off my face so I learnt to smirk instead Tess Christian

‘After Stevie’s birth I was overwhelmed with joy, but still didn’t feel the need to smile,’ adds Tess. ‘By that stage, keeping a straight face had become second nature.’

She and Nigel married in February 1993. ‘Of course, the wedding photographer was urging me to smile for the pictures, but I refused,’ she says. ‘It just wasn’t me.’

By the time Tess — who divorced in 1998 — reached 40 she realised that while friends had developed lines around their mouths, her skin was wrinkle free: ‘It dawned on me that I looked younger because I’d spent my life not smiling.’

At her London home, Tess has mastered the art of laughing inwardly at TV shows such as Absolutely Fabulous. But even after years of practice, remaining poker faced in public isn’t always easy.

‘My friends have nicknamed me Mona Lisa, after the da Vinci painting,’ she says. ‘Mona Lisa was said to have been quietly amused, as am I. I just won’t show it. Recently, an interior designer friend was telling me how a Spanish client kept referring to the department store John Lewis as “Juan Lewis”. I found it hilarious, but kept a straight face. I never crack.’

Thanks to her unwillingness to smile, Tess's friends have nicknamed her the 'Mona Lisa' after da Vinci's famous painting. Tess is pictured here in 1985, aged 23

The men she dates, meanwhile, often ask her to smile. ‘I assure them it’s not because I’m not interested,’ she says. ‘My pet hate is men who call out, “Cheer up, love, it might never happen,” ’ in the street. ‘I wouldn’t dream of criticising their appearance.’

Tess insists Stevie, now 24 and a film production assistant, has never been offended by her mother’s refusal to smile. ‘She is the opposite of me — she has a pretty smile that, of course, I would never stifle,’ says Tess. ‘She knows my sullen expression doesn’t mean I don’t enjoy her company.’

But London-based psychologist Amanda Hills says smiling is crucial to our mental health. ‘When you smile you release endorphins, known as “happy hormones” that make you feel good,’ she explains. ‘Not only that, but the more you do it the happier you feel, because you are telling the neural pathways in your brain you are happy — even if you aren’t.

Tess, pictured in Gordon's Wine Bar in 1985, says her pet hate is men calling out 'Cheer up, love, it might never happen'

‘Your brain doesn’t know if you are faking a smile because it’s just picking up muscle movement. Studies have shown you can increase happiness by smiling, even if you feel unhappy, which is why some medical professionals treating depression tell patients to practice smiling in the mirror.

‘Not smiling, meanwhile, has the opposite effect. A resting face with no emotion won’t allow your brain to pick up the signal that you are happy. And just as smiling attracts people, looking miserable is likely to deter them — which obviously risks making you feel miserable, even if you were happy in the first place.’

Tess (pictured) says even after years of practice, remaining poker faced in public isn’t always easy.

This doesn’t deter Vicky Kidd, 38, however. A textile designer from Hastings, Sussex, she started curtailing the amount she smiled five years ago after splitting up with her partner of eight years, with whom she has a son, Hayden, nine.

‘The lines on my face were escalating and with advancing age I started worrying about being left on the shelf,’ she says. ‘I felt most men wanted younger women and was paranoid about the competition from them.’

She was inspired by a yoga class she attended when newly single. ‘I was taught that “resting” my face by relaxing my facial muscles could minimise wrinkles and make me look ten years younger,’ she says.

Vicky Kidd, 38, noticed the lines on her face increasing five years ago and decided to limit the amount of time she spent smiling

‘It was recommended that we practice this for ten minutes a day, but I decided to go one step further and smile as little as possible. As I have big cheeks I’ve always felt I look like a horse when I smile, and it makes the skin under my eyes go baggy.’

Vicky, a vivacious woman who is adamant she is happy inside, explains: ‘It’s not that I don’t have emotions but I think there is a common misconception about smiling — often facial expressions can be used as a mask and the happiest looking people are the most miserable.

‘Men I’ve dated have been daunted until they realise I’m quite light-hearted underneath and strangers have called me a “grumpy cow”. But as I have consciously decided not to smile I can’t take offence.’

Vicky Kidd, pictured left aged 19, and right aged 6, on holiday in Devon. Vicky was inspired by a yoga class she attended which taught that relaxing your facial muscles could minimise wrinkles

Yet she admits: ‘I know I can come across as aggressive before I’ve even opened my mouth. The other day I had a misunderstanding with my son’s violin teacher about which day his lesson was on. When I asked for clarification she flew off the handle because she thought I was furious, when I wasn’t at all.’

Unlike Tess, she is prepared to bend her rules. ‘If someone beams at me I will smile back, so as not to appear unfriendly,’ says Vicky. ‘And I smile at Hayden when he is being funny because I would hate to hurt his feelings. But I refuse to exacerbate my wrinkles by manufacturing an artificial smile or laughing when it’s not necessary. And most people tell me I look much younger as a result.’

But there are also experts who disagree about the anti-ageing benefits. Julia Anastasiou teaches face yoga — a form of facial massage designed to keep skin line-free by stimulating the muscles underneath. She is a firm believer that the physical act of smiling promotes a youthful appearance.

Vicky (pictured) admits that sometimes she doesn't come across as happy when she is, and has struggled on dates in the past until men have realised she's actually very light-hearted underneath the facade

‘Keeping your face still to avoid wrinkles is misguided and won’t help at all,’ she says. ‘Wrinkles are caused by a lack of muscle tone and elasticity. Smiling massages facial muscles, which increases circulation and helps plump the skin’s connective tissue.’

Of course, smiling is not the only facial movement to alter the underlying muscles — frowning can also affect them. For this reason Christyne Remnant, 70, has refrained from furrowing her brow since the age of eight — and credits her youthful appearance to this. ‘I vividly remember watching my grandmother with a group of her 60-something friends,’ says Christyne, from Southampton.

‘Their foreheads were filled with lines that I could see got worse when they frowned. I decided then and there that I didn’t ever want mine to crease in the same way.

Christyne Remnant, 70, has taken an opposite approach and says she hasn't frowned since she was eight-years-old to prevent lines appearing on her forehead

‘It very briefly occurred to me to stop smiling as well, but I decided that would be a step too far.’

She adds: ‘Nobody thought it was strange, or even noticed, as I grew up — I was just known as a happy child. When I saw friends start to develop lines on their foreheads in their 20s, I became surer than ever that I’d made the right decision. And the longer I went without frowning, the more alien it became to me.’

Remarkably, she says that abstaining from frowning soon became so entrenched in her psyche that she didn’t find it difficult at all. She didn’t frown when she took her driving test aged 32; during childbirth to her three children: Justine, 45, Marcus, 44, and Belinda, 26; or even when her mother died, when Christyne was 59.

Christyne, pictured aged 22 (left) and 13 (right), says the longer she went without frowning, the more alien it became to her

‘Of course I’ve been through the same difficult and depressing times as everyone else, but I simply cry if I’m upset and grit my teeth if I’m cross,’ says Christyne, who is the director of a property development company owned by her husband Douglas.

‘I’m probably misconstrued as being more easy going than I actually am. I’m certainly not always happy — I get irritated by queues, smoking and people leaving doors open. But it would be very hard for me to frown when I’m angry now.’

Christyne (pictured) says she may often be misconstrued as being more easy going than she actually is, but says it would be hard for her to frown when she's angry now

Christyne’s scowl-free strategy seems to have paid off. Untouched by the surgeon’s scalpel, she could pass for a woman two decades younger.

‘People are always surprised when they find out how old I am,’ she says. ‘I don’t use face creams and would never have Botox. In any case, not frowning has worked better for me than anything cosmetic surgery could do. Using your facial muscles definitely marks your face.’

And for some women, that clearly is no laughing matter.