Tattooing has never been more mainstream. What motivates these people to permanently decorate their skin?

• Getting a tattoo is becoming a more common way of expressing individuality

Her coltish body is adorned with several large and elaborate tattoos. A peacock dominates her right arm, beginning on her shoulder and concluding with a beautiful feather on the back of her hand. The bird shares its roost with flames, a rose, a heart, nautical stars and a naked angel.

Hoy estimates she has around 2,000 worth of tattoos. Each is resonant with personal meaning. The crown and song lyrics on her left arm are for her husband. Her large "chest-piece" – including a huge golden key running from sternum to stomach – is an expression of love for her six-year-old daughter.

"I think there's something romantic about tattooing," she says. "The fact that it's my family, my husband, people I hold really dear, being under my skin. If you know in your soul the feelings you have for somebody, it shows an awful lot of courage to have that tattooed. I would be really honoured to have my name tattooed on someone."

Hoy is a vivid example of a general trend. According to one survey, a fifth of all British adults have tattoos. Many tattoo artists will tell you the majority of their customers are now female.

In Scotland, the scene is booming. There are now 38 tattoo studios in Glasgow; in 2005, there were 13; in 1985 there was just one. The figures will be similar for Edinburgh. But tattooing is not confined to the big cities. There are studios in Kirriemuir, Lanark, Montrose, wherever.

It has become mainstream, driven by TV shows such as Miami Ink and the example of celebrities well known for their tattoos, notably David Beckham and Cheryl Cole. In an era of reality television and online social networking, we are in the right place culturally for tattooing to take off.

The idea of looking and being looked at is one with which we are far more comfortable than we would have been a decade or so ago.

Indeed, the popularity of tattooing has become so widespread, there is concern that it is in danger of losing something of its underground artistic cachet.

Paul Slifer, tattoo artist at the highly regarded Edinburgh studio Red Hot and Blue, says he always tries to talk customers out of copying the designs of celebrities. "We want people to think for themselves. I know a lot of tattooed people who find tattooing offensive now. It's almost becoming lowbrow culture. It appeals to a lot of people, sure, but a lot of horrible shit appeals to a lot of people as well."

In Lucky Cat Tattoo on Glasgow's Great Western Road, Paul McCrorie, a 26-year-old PhD student, is stripped to the waist in readiness of having a geisha girl tattooed on his back. He booked an appointment two months ago with the artist Kevin Younger.

"I've been excited for the last four days," says McCrorie. For him, as for many people, the finished tattoo is not the be-all and end-all; the experience of getting inked is a sensory pleasure in itself. The smell of antiseptic. The insistent, insectoid drone of the needle. "I suppose we've all got masochistic tendencies," he says. "There's something about the pain."

Kevin Younger is a quiet, intense 43-year-old with longish, glossy black hair. He dresses smartly in tartan waistcoat over white shirt and describes himself as a "gentleman tattooist".

His studio, for which he prefers to use the old term "parlour", is decorated in deep red and dark wood with vintage posters and a big statue of Christ. Large windows show it off to the street. Younger's clientele are very mixed, from accountants to rock stars. He is well known for his work with Simon Neil of Biffy Clyro.

McCrorie's geisha is a three-hour appointment. Tattooing, done well, is a slow business. An arm – or "full sleeve" – could take up to 40 hours spread over months of appointments.

Most studios charge between 70 and 100 per hour. Some of the industry's most celebrated artists can name their price and be assured plenty of people will pay it.

Watching Younger work is fascinating. He's so focused, leaning in close over his client's bent back. "This isn't a job," he says, "it's almost an obsession. I never switch off."

The small, warm space in which he works has a look and atmosphere somewhere between a doctor's surgery and painter's studio. Tattooing is, in truth, more craft than art. The tattooist is similar to such fading tradesmen as the cobbler, blacksmith or master butcher. What's required is knowledge, experience, flair and patient absorption in the work.

As Younger tattoos McCrorie, the needle penetrates the skin to a depth of about one millimetre. Tattooing is an intimate process. You are right inside someone's personal space, literally breaking through their barriers for a prolonged period. It is not unusual for tattooist and client to become close friends; collaborators and confidantes.

"The human body is the ultimate canvas," says Younger's apprentice Frenchie, a pretty 22-year-old with pink hair and eyebrows. "If you do a painting it can be stuck away in a cupboard. But we're putting something on somebody who's going to wear it forever. It's amazing that someone is willing to put that trust in you."

For proof that a great many people are doing just that, look no further than the Scottish Tattoo Convention at the Corn Exchange in Edinburgh. Over 100 artists have set out their stalls and are busy inking a good proportion of the 3,000 visitors.

The swarming buzz of needles can be heard quite clearly over the music on the PA – Johnny Cash, AC/DC and their outlaw ilk – and is not even quite drowned out by the compere, Pedro Machado, as he calls competition entrants on to the stage to have their tattoos judged: "And here's Crystal with a – what is it Crystal? – it's a zombie Virgin Mary! Show some love, people!"

You don't have to be in the market for a tattoo to enjoy the convention. Most of the tattooing genres are represented: traditional with its swallows and daggers; Japanese – all intricate demons and waves; tribal and Celtic; photorealist black and grey. A nerdophile girlfriend gently wipes away the blood beading on her boyfriend's new Star Wars tattoo.

There is a personal appearance on stage by Elaine Davidson, a Brazilian now living in Edinburgh, who is the most pierced woman in the world. She has 6,925. Her face is a mass of metal rings below a candyfloss pile of hair. What age are you, Elaine? I ask. "Old enough to play with you," she replies. "Are you old enough to play with me?"

Brad Oliver, a 55-year-old bus driver from Kelty, is lying face down on a table as Morag Sangster, owner of Glasgow and Edinburgh's Tribe studios, tattoos his right leg. They have been working together since 1996. Tattoo artists must understand musculature and the different textures of skin, Sangster explains. "The elbow," she smiles, "is a design challenge."

Oliver's right leg shows the iconic image of the young girl Kim Phc running naked away from her burning village during the Vietnam War. It also features the Enola Gay bombing Hiroshima. Oliver is planning to have Picasso's Guernica tattooed on his other thigh. He is a former squaddie who served in Ireland during the mid-1970s, but is now anti-war. "What you wear on the outside reflects who you are on the inside," he says. "You're wearing your heart on your sleeve."

On the other side of the room, a young woman has cherries tattooed on a chest that runs more to melons. There is a great deal of thigh and cleavage on display, a fact that has encouraged attendance by a few older gentlemen whose interest in the art does not seem entirely pure.

"I like your legs," they assure those who catch their feverish eyes. Their enjoyment of the occasion is by no means compromised by performances from burlesque dancers.

One of the performers, Daiquiri Dusk, speaks backstage. "When I was younger, I was involved in self-harming, and my first tattoos basically came out of that.

"I was getting them done as a way of feeling in control of pain. But it's different now. They have more meaning." She pulls back her hair to reveal, behind her left ear, a tattoo of herself wearing the outfit she has on today.

"I'm whispering to myself that I should aim higher."

Upstairs on the balcony there is an exhibition of vintage "flash" – the name given to those standard designs shops offer to customers. The most striking piece is a large image of William of Orange riding his white charger at the Boyne. It was drawn in 1986. Most studios these days will refuse to give sectarian or otherwise bigoted tattoos.

A man wanders over. Davey Mitchell is 69 with a hearing aid and a baseball cap. He is covered in tattoos that have the fuzzy blue look that comes with age, but the eagle's head on the right side of his neck is fresh. He bends to examine King Billy.

"Terry put that on my back when I was about 28," he says, "and it was the worst thing I ever did. You'd go to Castlemilk baths and get kids spitting on you."

Mitchell got his first tattoo at 15. It was a love heart and the man who did it was Bert Vallar. The Vallars were the fathers of Scottish tattooing. Prince Vallar, born Patrick Henson in Derry, began tattooing in Glasgow in 1918 and set up Scotland's very first tattoo studio, at 404 Argyle Street, in 1935. His sons, Bert and Stephen, took over the business in 1947.

What little there is known about the Vallar family comes courtesy of Terry Manton, a signwriter from Motherwell, who has been researching the subject for years and has published his findings on his website, princevallar.co.uk.

Manton, 45, is a former tattoo artist. He taught himself while still at school, opened a studio in Airdrie at the age of 18, but found the life unpleasant. To hear him speak is to understand the great distance tattooing has travelled from the scuzzy margins to the mainstream.

"Back in my day, you had to be tough," he recalls. "I actually carried a big iron knuckle-duster in the pocket of my white coat at all times. Sometimes customers would get a wee drink in them before they came up to the shop, and that could lead to trouble.

"One day, things got out of hand, and I got attacked by five guys. I pulled the knuckle-duster out and smacked one of them, and then we all piled into the corner. My neighbours were dressmakers, a mother and daughter, and they came in screaming, scratching and biting. They saved me. That was what it was like in those days. You could show no fear."

Downstairs at the Tattoo Convention, that seems a very distant era. Tattoos these days are art statements and personal expressions, no longer ways for hard men to prove themselves hard. A young man runs through the crowd, naked but for a pair of black Calvin Klein trunks he is only half-wearing.

"Ooh, slap his arse!" yells a portly woman as he passes. This is Thomas Weir, a 28-year-old structural engineer from Glasgow. He has just had a huge design of skulls, daggers and roses tattooed down one side of his body, including his right buttock.

"I love it. I think it's amazing," he says of his tattoo, which has taken 12 hours in total, four today, and includes the words "Always Remembered and Loved" on a scroll. "My dad died when I was 15 and he had a tattoo of a skull with a dagger through it. Mine is basically the same, just bigger. 'Always remembered and loved' is what it says on his grave plaque."

But it is such a huge tattoo. What happens when Thomas is an old man and rather less toned than he is now? "When I'm 70, I'm not going to be running about naked, and it will give me a story to tell. My grandchildren will be, like, 'Grandad's cool as anything.'"

The fact that so many people here have such extensive coverage, including in some cases their hands and even faces, is testimony to the addictiveness of getting tattooed. Stuart MacDonald is a 31-year-old from Musselburgh.

A former support worker looking after disabled children, he is a big, friendly, bearded man, a young, ginger Falstaff. He works on the front desk of Red Hot and Blue and would one day like to be an artist.

Despite being amiability itself – "I'm a nice dude," he says correctly – MacDonald often finds there is an empty seat next to him on even the most crowded buses. The reason is obvious. "Man, I've got a lot of tattoos," he says. "I would say I'm 95 per cent covered. Where would you like to start?"

One obvious place is his throat, across which he has a large tattoo of Jesus and Our Lady. "I'm not religious but thought it was beautiful and the most famous mother and son I could think of. My mum was ill with throat cancer, so it was for me and her."

It's interesting, this desire to record important moments in one's life with a tattoo. The body as a diary, perhaps, but it's more than that. Tattoos are essentially metaphorical. Their permanence makes them so. They symbolise commitment.

A tattoo in honour of a dead father or a newborn daughter is a promise to remember, or to nurture and love. They are under the skin but visible, so they are about the inner life of emotions but also the outer life of action.

They say: this is how I feel and this is how I will act. They are a promise one makes to oneself and the world.

In the old days, sailors would get particular tattoos to indicate the extent of their travels: an anchor showed the seaman had sailed the Atlantic; a turtle meant he had crossed the equator. These days, the tattoos we wear have a similar purpose – symbols of how far we have navigated on life's voyage, the joyous ports in which we have sheltered and the storms of grief we have endured.

But of course there is a far simpler way of explaining their appeal. Laura Hoy puts it best. "The absolute bottom line," she says, "is that I love the look of ink on skin."

This article was first published in Scotland On Sunday, 3 April, 2011