"Sam" never had a problem with the size of his penis, but after he ended his 16-year relationship, he wanted to do something to boost his self-esteem.

Key points: A new study has looked into why men undergo penis enlargements

A new study has looked into why men undergo penis enlargements Most men say they want to feel better about themselves

Most men say they want to feel better about themselves No data is collected about the procedure, but surgeons say more men are expressing interest

"I definitely didn't feel small, but I wanted to feel an extra confidence, something extra special — especially if I was going to be going back onto the dating scene again," he said.

He researched surgical penis enlargements, but he was wary of the potential pain and risks involved and decided not to go ahead with it.

But when he learnt that dermal fillers — normally used to plump up lips and cheeks — could also be used to enhance the girth of the penis, he booked in to see a plastic surgeon.

"I was at a bit of a loose end at the time, and I had some cash lying around so I thought I would give it a go," he said.

Sam spent about $10,000 on temporary fillers, and 18 months later, he is happy with the result.

"I would definitely do it again. But on the psychological side of things, it was interesting. It was a bit of a double-edged sword," he said.

After the procedure, Sam struggled with performance anxiety during sex.

"Maybe it was a bit of expectation from my partners, or a sense of having to follow through with the goods. It took me a while to feel comfortable with that part of it," he said.

'Penis size really taps into men's sense of self'

Cosmetic surgery is often thought of as a woman's pursuit, but surgeons said they were seeing more men book in to discuss penis enlargement.

That trend inspired Monash University clinical psychologist Dr Gemma Sharp to study what drove men to undergo the procedure, and how it impacted their lives.

She and her co-author, Dr Jayson Oates, interviewed 25 Australian men who underwent a non-invasive enlargement in the last 12 months.

It was a qualitative study, which focused on in-depth interviews. This kind of research is often done on emerging psychological trends.

"I was surprised by the diversity. In our sample, the youngest man was 23 and the oldest was 69. They were coming from all different types of professional fields," Dr Sharp said.

"I suppose that penis size really taps into men's sense of self, no matter what else is going on in their lives."

"Women are surprised to learn that men have body confidence issues as well," Dr Oates said. ( Supplied: Jayson Oates )

The researchers found the vast majority of men underwent the procedure to improve their self-esteem — and many were particularly worried about how other men perceived them.

"The locker room syndrome is either trying to impress other guys or trying to not feel self conscious in front of other men. But others were looking to please their sexual partners," Dr Oates said.

However, Dr Sharp and Dr Oates found that almost every man who took part in the study had an average-sized penis before they underwent an enlargement.

"We're not exactly sure how they got the impression that they were on the smaller side," Dr Sharp said.

"I think it probably goes to show that the genitalia shown in pornography is on the particularly large side, so everyone would feel inadequate compared to them."

They also found that Sam's experience with performance anxiety was not unique.

"Some thought that potential sexual partners would think they were an absolute star in the bedroom because their penis is now big. So I think the effects on sexual relationships were a little bit more mixed," Dr Sharp said.

The study is one of the first of its kind to investigate why men are undertaking cosmetic surgical procedures.

Researchers said while there had been studies into women's motivations, little was known about what drove men to cosmetic treatments.

"A lot of women are surprised to learn that men have body confidence issues as well," Dr Oates said.

All kinds of cosmetic procedures, including those on genitals, have become much more popular in Australia in the last few years, according to Dr Sharp.

Their study found that two out of the 25 participants had a condition called body dysmorphic disorder — a psychological condition in which a person becomes obsessed with imaginary defects in their appearance.

She found some of the men in the study had previously had other cosmetic procedures including anti-wrinkle injections, and more than a quarter had previously tried other forms of penile augmentation.

Their research paper is about to be published in the Aesthetic Surgery Journal.

Cosmetic surgery is becoming more acceptable for men

Dr Gavin Scriven and nurse Madeline Firkins perform non-invasive penile augmentations in Sydney. ( ABC News: Rebecca Armitage )

Dr Gavin Scriven performs dermal filler injections to the penis at his Sydney clinic.

No national data is routinely collected in Australia about cosmetic surgery trends.

But Dr Scriven has noticed an increase in the number of men coming to see him since the non-invasive procedure came to Australia five years ago.

"We've treated hundreds and hundreds of men here. A lot of the guys I see are not particularly distressed about their body image, but they're just seeking some self-improvement," Dr Scriven said.

Before then, men seeking a penis enlargement had to undergo major surgery to break the ligament below their pubic bone.

That procedure involved six months of recuperation, and cost up to $15,000.

But Dr Scriven said he believed it was also becoming more acceptable for men to undergo cosmetic procedures.

"It probably isn't so accepted for a man to get cosmetic surgery as it is for women, but it's definitely becoming more common and less taboo," Dr Scriven said.