'What has this person done?': Specialists alarmed by tanning trend

Lisa Byrom says the trend seems to be most prevalent in teenagers and those in their early 20s. (ABC News: Mark Leonardi)

Skin specialists are sounding the alarm over potential cancer risks associated with unregulated peptides at the heart of a social media-driven beauty craze.

Dermatologists have told the ABC they have seen patients who used Melanotan-II suddenly developing new, abnormal and potentially dangerous moles while taking the peptide.

Skin doctors are urging patients who may be worried after using unregulated peptides to book a skin check.

When a teenage boy lifted his shirt, his mates were horrified by what they saw.

Confronted, his friends urged the boy to show his parents and a doctor.

When dermatologist Lisa Byrom saw the boy's "atypical, worrying" moles, she was overcome with emotion.

She was deeply worried that the boy's moles might be early melanomas.

The boy had been injecting an unregulated peptide, melanotan-II (MT-II), to give himself a tan.

Large moles similar to these appeared on the young person's back after they used melanotan-II. (Supplied)

His skin darkened but Dr Byrom said the patient also "developed lots of funny-looking moles, all over their back very, very quickly".

Those "really atypical" moles deeply concerned Dr Byrom and she cut some out immediately.

The results were negative for melanoma, but the number of abnormal moles on the teenager's back would be a lifetime worry, Dr Byrom said.

"They are now at an increased risk of melanoma … for the rest of their lives."

The latest wellness craze to take social media by storm is fuelling a growing grey market of injectable peptides in Australia, and it has experts worried.

MT-II is a synthetic peptide, unapproved for human use or sale in Australia.

Some of Australia's most senior skin doctors told the ABC they had seen a growing number of patients present with worrying side effects — including multiple atypical moles, a known risk factor for melanoma — after using MT-II.

"It's essentially tricking our skin cells to believing that it needs to produce more pigment, so it fast-tracks skin darkening," dermatologist Leona Yip said.

"It's not just a wellness or cosmetic product that you use and it's banal and it's harmless … it's not."

Before and after images of a person using melanotan-II. (Supplied)

Doctors have been issuing warnings about MT-II for a number of years.

Despite those warnings, there has been an explosion in popularity of unregulated injectable peptides in Australia, driven by social media users promoting their supposed benefits for health and b