UNA Morrison arrives with a small, colourful box tucked under her arm.

She gestures to a space at the end of the sofa. "Is it OK if I sit Samantha here?" she asks, setting it down.

Samantha is her wig. Una lifts the lid to reveal a cluster of silky, blonde hair nestled inside. Almost a year has passed since Una's hair began to "fall out in clumps". Diagnosed with breast cancer, the 48-year-old finance worker from Irvine, Ayrshire, underwent four months of chemotherapy.

Her story is charted in a documentary, My New Hair, which will be shown on STV this Monday. She is joined in the powerful film by a clutch of other women including Helen Hosie-Kallstrom, who like Una has battled breast cancer, and Jo-Anne Jackson, who has been affected by alopecia from the age of three.

Filmmaker and director Ruth Carslaw came up with the idea after a visit to Francis Hair and Beauty in Galston, Ayrshire. Her interest was piqued by a series of portraits on the wall. "I asked about them and they told me that all of the women in the photographs were wearing wigs," she says.

Delving further into the subject, Carslaw says she was blown away by the sheer volume of women visiting the specialist salon to be fitted for wigs. She decided to document their stories and confront head-on society's taboo about hair loss.

Over the months Carslaw forged close bonds with the women she filmed, accompanying them on an intimate journey. "You are with someone at such a massive moment in their life," she says, her voice catching with emotion. "You lose yourself and you find yourself. It does change you. When you lose that part of your identity, it's traumatic.

"The whole idea of the film was that the camera would act as a mirror. I wanted it to be bold. There is a strength that comes from the women taking part. When they agreed to be in the film they all told me: 'I'm doing this because I don't want any other woman to feel alone.'"

Carslaw has personal experience of the issue after suffering hair loss during her twenties. "It was a long time ago and my hair grew back," she says. "I was ill and abroad. It was a frightening experience to be in the shower, thousands of miles from home, with my hair coming out in clumps. I remember being really scared."

One of the first women she met researching the show was Helen who had recently begun chemotherapy for breast cancer. "We spoke in a cafe and that same night she sent me a text message with a picture of her hand holding a clump of hair," recalls Carslaw. "I filmed Helen with her twin sister, Claire, who is a hairdresser, as she got her hair shaved off. That was the start of the journey."

When Helen, 36, was diagnosed with cancer in January last year her first question, she says, was to ask doctors if she would die. "My next question was: 'Am I going to lose my hair?'" she says. "I already knew I wanted the breast off but losing my hair felt different."

Helen, a music journalist from Kilmarnock, started chemotherapy four weeks after having a mastectomy. "I had lovely, long red hair and I made the decision to cut it up to here," she says, gesturing above her chin. "That was the first step because I knew I was going to lose it all.

"I went to meet Ruth to talk about being in the documentary and that same night my hair started falling out. I stood in the shower and the more I touched it, the more fell out. I lay in bed that night scared to move.

"The next morning it took 45 minutes to clean up all the hair. I had a giant bald patch where it was gone completely." She pauses, collecting her thoughts. "If I cry here, I'm sorry," she apologises unnecessarily.

"My twin sister is a hairdresser and I asked her to shave off what was left," continues Helen. "I thought I was ready for it but the minute she put her hands on my head I said: 'Wait'. I remember thinking: 'My God, I'm going to look like a monster.' I had one breast and no hair; I knew my eyelashes were going to fall out. It was a horrible feeling."

In the film, we see the raw emotion as Helen's hair is shorn away, tears cascading down her cheeks. Her sister Claire is tasked with the clippers as husband Frecko looks on helplessly, the pain visible in his eyes. "It was hard because I didn't just feel it for myself, I felt it for my partner and also my sister who had to shave it off," says Helen. "I never coped with the full hair loss. I always covered my head. I didn't like anyone seeing me without hair. Even the thought of it freaked me out."

Helen, who has two sons, is able to eloquently articulate the grieving process. "My hair was a big part of my identity," she says. "I'm a twin and you fight for your own identity. I felt like I'd been stripped of that. It was suddenly: 'Do you know Helen, the bald one who has had cancer?' I felt I had gone from being one person to this shell I didn't want to be."

It is an experience that Una can relate to. "I was told the second chemo session would be the hair loss one," she recounts. "A day later it started. People say your hair falls out in clumps but I wasn't ready for what that was actually like. I woke to find hair on my pillow then as I moved around the kitchen that morning it was falling everywhere."

She called the salon and said: "I need to come now." Una, who has a 17-year-old daughter and is engaged to Campbell, 46, had already been fitted for her wig - aka Samantha - and that afternoon had her head shaved in preparation for wearing it for the first time.

"In the weeks afterwards I would get up in the morning, catch sight of myself in the bathroom mirror and do a double take," she says. "I would sometimes forget for a moment that my hair was gone."

Helen sitting nearby nods in agreement. "I got rid of every mirror in the house," she says. "I could look in the mirror and my mastectomy scar didn't bother me - it still doesn't - but having no hair did."

Una recalls having to break the news about her cancer to her 88-year-old mother, who lives in Cork. "I come from a family of six girls and four boys. My mother was always obsessed with how her girls looked. We all had the long, blonde hair," she says. "There were times I would go to visit her and she would say: 'Oh Una, your hair is your pride and glory.' It was always about the hair.

"I went home last September to tell her about my cancer and had my wig on," she continues. "We were in the living room and my mum said: 'Una, there's a beautiful shine to your hair.' My partner Campbell, who was sitting next to me, almost spat out his coffee. She asked me: 'What kind of shampoo do you use?' and I quickly replied: 'Tresemme' because I didn't want to blurt it out.

"I got up the next morning and went downstairs to tell her. I was shaking as I started to speak. I said: 'I've had a bit of a year, I wasn't too well. This isn't my hair, mum. I was diagnosed with breast cancer.' She immediately said: 'What? Take it off, take it off.'

"I remember pulling off the wig and my mum start howling. She said: 'Please, put it back on'. So I did. She asked to see where my breast had been removed so I pulled down my nightie to show her."

Una staunchly wore her wig for the remainder of the weekend. "My mum, being 88, had the heating on morning, noon and night. I had to keep going to the bathroom to take the wig off and open the window to cool down. Sometimes I'd come back out and it would be sitting a funny way." She gives a small chuckle, recalling the absurdity of the moment.

Her hair has started to grow back and today frames her face in curly, blonde tendrils. Samantha, meanwhile, has been happily retired although Una vows to always keep her around "unless some other woman needs her". Her gaze flickers towards the box containing the wig. "Hopefully I will never need to put her on again," she says.

For Jo-Anne Jackson, life without hair is all she has ever known. The 19-year-old from Troon was three-and-a-half when her hair started falling out. "I've seen photographs of when I had hair but I don't actually remember what it was like," she says. "I had a few wigs growing up but they were really old fashioned so I didn't wear them much. It never bothered me, though, because I haven't known anything different."

Jo-Anne has alopecia, the general medical term for hair loss. "There are different kinds and I have universalis which is all body hair - I have no eyelashes or eyebrows," she explains. "Alopecia affects people in different ways; with some it's facial and head hair, others lose their hair in patches."

She was fitted for her first proper wig at the Galston salon aged 15 and now works there as trainee hairdresser. While Jo-Anne has developed a wonderful nonchalance to dealing with her hair loss, she can still relate to the tumultuous journeys experienced by many of the women in the film.

"It's easy to say: 'Don't worry what other people think' but it still hurts when a stranger shouts something at you in the street," she says. "I would rather someone came up and asked me if I was wearing a wig rather than hear the whispering. I don't understand why there is still such a stigma."

While My New Hair is moving and at times sad, it is filled with wonderfully uplifting moments. Not least the story of another youngster, Morgan Paterson, who has had alopecia since she was six.

The camera follows Morgan, now nine, as she joyfully twirls in a chair after being fitted with her new wig. Afterwards we see her revel in the freedom of being able to go swimming again, basking in the water like a mermaid with her long red tresses fanned out around her.

Then there is the tender love story unfolding between Helen and Frecko, 40, who got married last month. We witness the exquisite happiness as Helen is fitted for her eye-catching purple wedding dress and the unabashed jubilation as she finishes her final chemotherapy treatment.

"I hope this film makes people more aware and less ignorant," says Helen. "I remember going to Asda and hearing a woman whispering: 'That lassie is bald' and I could happily have shaved her hair off and said: 'Walk a mile in my shoes.'"

Helen has set up a Facebook page to offer support to other women experiencing hair loss. "I regret hiding my hair loss now," she says. "I would say to anyone: don't hide it. Be vibrant, be the person you are."

My New Hair will be shown on STV on Monday at 8pm