After decades of scientific debate, what is known as the facial feedback hypothesis, or FFH, has finally been universally confirmed among psychologists.

The theory states that smiling can make you feel happier and increase your mood.

Likewise, frowning has the potential to make you feel sadder.

Just how such a simple trick can subtly improve your mood has finally been confirmed by a recent international study, agreed upon by proponents and skeptics alike.

Intriguing studies carried out in the 1980s showed people who had to hold a pen in their mouths found stand-up comedy to be far funnier than those who did not. The reasoning behind this was that holding a pen, without letting the lips touch, meant that facial smiling muscles were activated. That act sends positive signals to the brain and reinforces emotions.

More recently, an international study carried out this year recruited more than 4,000 people to investigate the idea further. The participants were divided into groups, with one group told to move the corners of their lips to their ears and raise their cheeks using only the muscles on their face. Volunteers then rated their own happiness as they pulled the faces. The increase in happiness in those told to activate their smiling muscles was equivalent to being shown images of puppies, kittens, or flowers — a subtle but measurable increase.

The study, carried out by researchers from Stanford University, suggests happiness and mood in general has at least some basis in the physiological as well as psychological.

Somewhere within the complex interaction between our brains and our bodies is the key to regulating our mood and our states of happiness. Physiological responses to negative emotions, such as increased heart rates, and skin temperature, can indeed also be altered, when people adopt more positive facial expressions.

The so-called modification studies have found that volunteers even believed bad smells were not as repulsive when they were forced to hold a positive facial expression.

The age-old saying "fake it till you make it "seems particularly applicable to our state of mind.

Difficulties in these kinds of studies, however, stem from the fact that it is intrinsically challenging for people to self-monitor their own mood reliably. What could be one person's "7 out of 10" on the happy scale may be experienced wildly differently by another. Measuring physiological markers of stress or relaxation is, therefore, a more reliable objective marker of how we feel. Markers, such as pupil dilation, muscle tension, sweating, and the presence of goosebumps on our skin, can all betray our internal feelings, even if our faces give away no secrets. These readings can help decide just how much of an effect simply smiling can achieve.

Collaborative scientific efforts have now led to the generally agreed upon consensus that the facial feedback hypothesis works. Indeed, some studies indicate that the greatest effect of FFH is to amplify a mood that one is already feeling. Smiling therefore can compound existing positivity.

Scientists have found that people who often smile and laugh easily when interacting with others tend to score higher on wellbeing charts. The research around mood modification studies are becoming ever more convincing, meaning that they could persuade others to laugh and smile just a little more in everyday life.

Barry He is a London-based columnist for China Daily.