Camilla, 31, felt a little out of place at university. She made a few very close friends, but avoided the rowdy pub crawls loved by her peers and was reticent at seminars. Now, 10 years on, she holds back during work meetings (she's a web designer), but is happy to send her colleagues reams of ideas by email. Every weekend she potters round her flat listening to music, cherishing having a whole quiet day at home, leaving her free to think, read and be.

It's fair to say that Camilla is a typical introvert, and if this sounds like you, rest assured that you're not alone: between a third and half of the population are introverts, too. You might think you're in a minority, but that's only because you make less noise.

‘The classic definition of an introvert is that when you're out and about, even if you're having a good time, after a while you feel drained and want to recharge by yourself,’ says Susan Cain, self-confessed introvert and author of Quiet: The Power Of Introverts In A World That Can't Stop Talking. ‘Extroverts, however, recharge through stimulating situations such as the proverbial loud party. What's really happening is that introverts and extroverts have preferences for different levels of stimulation.’

Studies have shown that introverts are physiologically more sensitive than extroverts – they sweat more in reaction to stimuli such as noise and emotions, and salivate more in response to a drop of lemon juice on the tongue. ‘These reactions transmit into subtle signs that are not necessarily perceptible in a social setting – a quick aversion of the eyes before you shake hands with someone new, for example,’ says Cain. ‘It's only in the lab that we can pick these changes up.’

In short, introverts react more strongly to stimulus and therefore need much less of it or they rapidly become overstimulated. ‘When overstimulated, an introvert’s mind can essentially shut down,’ says life coach Nancy Okerlund of introvertenergy.com. ‘It becomes hard to think, hard to make light conversation, hard to feel comfortable, even in a room full of close friends.’

Introverts thrive in a lifestyle that provides frequent opportunities for quiet, ‘and even solitude doesn’t necessarily guarantee downtime’, she says. ‘Sometimes downtime means giving the hard-working, complex introvert brain a rest from thinking, by smelling the flowers or staring out the window at a cloud.’ Introversion shows up early in life.

In a seminal study, American psychologist, Jerome Kagan, identified 'high reactive' four-month-old babies as nascent introverts. These babies reacted strenuously to new experiences, thrashing their limbs about and crying when they saw new faces or objects or experienced new smells. They were found to have over-active amygdalas (the part of the brain that triggers the adrenalin response to danger) so were easily overstimulated. As they grew up, Kagan found these babies became quiet and careful children and teenagers. Although introversion is a common enough characteristic, our society is becoming increasingly hostile to it. In the US, a profoundly extroverted nation, parents seek professional help if their children are quiet, and these children find themselves diagnosed as suffering from 'social anxiety disorder'.

Even in the UK we're fascinated by a never-ending parade of pop culture extroverts. It's this lionising of extroversion that Cain has dubbed the ‘extrovert ideal’ – despite the fact that there are many high-profile introverts who have made their mark on the world, from Bill Gates, Facebook founder Mark Zuckerberg, and JK Rowling to Jodie Foster and film director Ang Lee. ‘The “extrovert ideal” is the cultural phenomenon where in our schools, workplaces and religious institutions, we revere people who are bold, entertaining, alpha and gregarious, and appreciate far less a different constellation of traits – the serious, reflective, cerebral characteristics associated with introversion,’ says Cain.

However, she points out that these serious traits are greatly admired in some countries, such as China, where shy and sensitive children are popular at school. While introverts are easily overstimulated, in one particular way they are less easily enlivened: the dopamine pathways of an introvert's brain are less active than the corresponding pathways in the brain of an extrovert. So they are less susceptible to the euphoric dopamine 'buzz' we experience when we achieve our goals.

‘Extroverts have stronger 'reward networks' in the brain, fuelled by the neuro-transmitter dopamine, and it is these networks which make us sensitive to rewards such as going after promotions or winning money,’ says Cain. ‘Extroverts experience excited feelings about chasing after markers of status. Introverts care about these things with less intensity so they are more careful and deliberate.’

Indeed, while extroverts get into more car accidents, introverts tend to make better investment decisions and take fewer financial risks. Academically, introverts generally outperform their extroverted peers – while at the same time exhibiting greater creativity. This link between introversion and creativity, says Cain, may be because introverts spend much of their time alone and this can solitude spark innovation. Or it may be due to the fact that introverts tend to be more persistent problem-solvers, giving up less easily than extroverts when faced with a tricky puzzle.

Although introverts have so much to give, they are often ill at ease in the workplace, where office life is increasingly structured to benefit the gregarious extrovert. ‘The majority of companies organise workers into teams and house their workers in open-plan offices with no walls and no privacy, even though these approaches have been proven to be less productive,’ says Cain. ‘Extroverts are also routinely groomed for leadership, although introverts are often better leaders than extroverts, delivering better outcomes, particularly when leading pro-active teams.’

Introverts duly learn that it pays to fake extroversion. In fact, some of us hide our introversion so well, we even hide it from ourselves. ‘Many people realise they're actually introverts who've trained themselves over time. They've never fully felt right, because they've always been stretching themselves,’ says Cain, describing a characteristic she calls 'pseudo extroversion'. ‘If you're an introvert, you often have to be a pseudo-extrovert for the sake of work you enjoy, or a person you love ­– and it can be fun to act outside your persona. But you need to limit how much and how often you do this.’

For advertising account executive Jane, 33, this rings all too true. She spends days locked in meetings, and when she's not making calls in the vibrant open-plan office, she's bantering over coffee or going for Friday-night drinks with the team. She comes home feeling drained, fit only for a long bath and sitting quietly in front of the TV. She knows that if she doesn't get to recharge quietly, she'll be totally unfit for another day of pseudo-extroversion at the office. As a result of this pretence, ‘there can be a fear of being “worn out” after a while – after all it’s a kind of acting,’ says psychotherapist Virginia Mallin. ‘The emotional wear and tear is considerable for anyone not living in a way that is true to themselves, as it takes up a lot of emotional energy sublimating parts of ourselves.’ Unsurprisingly, Jane is looking for another job. The misery caused by the clash between her character type and her work is typical of the fact that, as a group, introverts tend to be less happy than extroverts. This is partly due to the fact that they're inhabiting a system stacked against them.

Perhaps there's another explanation, too: we tend to define happiness in ways which are more easily experienced by extroverts. ‘An extrovert's stronger reward networks flood them with more dopamine, which is associated with upbeat exuberance and joyful types of happiness, so they reach that kind of 'champagne bubble' state more readily than introverts do,’ says Cain. Yet there are many other kinds of happiness that introverts relish. ‘For example, a transcendent state often reached in solitude called “flow”, where you are completely engaged in the task in hand, is a state many introverts often reach,’ says Cain. ‘And the “happiness of melancholy” – a shared expression of recognition that life is fragile, an acknowledgement of love, loss and yearning – can create a profound happiness. It's this subtle kind of happiness that introverts have a particular ability to share and understand.’

Once an introvert begins to grasp who they are, they'll be well on the way to their own kind of happiness. ‘As you begin to understand the physiology of introversion, reframe introversion as an asset and learn to manage energy skilfully, you start to become a “conscious introvert”,’ says Okerlund. ‘It’s an ongoing process, allowing one to thrive as an introvert – even in the challenges of an extroverted landscape.’

How to shine as an introvert in an extrovert's world: Susan Cain offers five strategies

1. Carve out 'restorative niches' throughout your day and build them into your life and work. Even at a party, make sure that you take time out somewhere quiet at regular intervals to recharge. This gives you room to be your true self.

2. Look for opportunities to have one-to-one conversations. Perceiving a cocktail party or networking event as a series of one-to-one conversations turns it into a forum where introverts can shine. Apply the strategy of quality, not quantity, and understand that one genuine new relationship is worth more than a handful of business cards.

3. Identify your 'sweet spot'. This is your ideal level of stimulation, leading to optimum energy. It will fluctuate throughout the day. If you’re feeling slightly uncomfortable, follow your gut feeling as to whether you need a more energising environment, or a quieter corner.

4. Make the most of social media. Introverts are great at using social media. Start a blog and you'll soon find yourself communicating with people all over the world – on your own terms. No matter how many windows you have open on the screen, it's still you sitting quietly with a computer and a cup of tea.

5. Be true to yourself. We can all act out of character at times. If you have an extrovert partner who yearns to socialise together, make a pact to go to a certain number of social events a month you're both happy with. Learn to act extroverted from time to time: stretch yourself, but know your limits, and be sure to plan time afterwards in which to recharge.