For some, the thought of a room full of strangers laughing their heads off at nothing will cause alarm bells to ring, triggering images of new age bearded hippies resplendent in tie-dyed clothes, socks and sandals.

However, a growing number of people are signing up to laugh en masse - at nothing - in the hope of a health boost delivered with a smile.

Laughter yoga, the therapy which promises every health benefit from a strong heart to a slim waistline, is not necessarily something to tickle everyone's funny bone.

However, its proponents say nearly everyone can benefit from having a good regular chuckle, and hope it will spread throughout the country, from the boardroom to the hospital ward.

Auckland-based Malcolm Robertson is a registered clinical psychologist who in 2006 did a five-day course in leading laughter sessions.

It took a while for the self-confessed cynic, and "scientific brain", to relax among a group of 25 all learning to laugh as therapy from laughing doctor Madan Kataria.

"It was definitely a life changing experience," Mr Robertson says.

Now, Mr Robertson leads a weekly laughter session in Ponsonby, Auckland, which he says has grown from a few friends and family to around 30.

He had long been interested in the beneficial effects of positive emotions on people's wellbeing, he says.

As a clinical psychologist, he says he knew "quite a bit" about what made people unhappy.

"Positive emotions tend to trump negative ones if we have them often enough," he says.

There is a vast body of scientific evidence to show regular laughter has health benefits - it relaxes the muscles, eases stress, invigorates the heart rate and improves the immune system.

What is interesting is that people seem to gain the same benefits whether they were genuinely laughing or just faking it.

"If you are faking laughing, the breathing and physical exertion is using exactly the same muscles," he says.

Whether a person is honestly tickled, or just going through the motions, the body experiences the same sensations and benefits - as does the mind.

"The body is trumping the mind by starting to laugh without any reason - it can actually make a person more joyful.