The American product Permatan has almost 90,000 followers on Instagram and promises users a permanent tan that lasts years.
Its website claims even those with the fairest of skin tones can achieve a long lasting dark tan.
Dermatalogical Society co-president Louise Reiche said the ingredients in Permatan are banned in the country.
"They contain a fundamental product called Melanotan II which is stimulating a particular enzyme of tyrosinase in the pigment cells and they're not legal in New Zealand but because people can purchase them online, it goes around those regulatory mechanisms," said Reiche.
She said Permatan sped up pigmentation which had the potential for increasing skin cancer risk.
Last year, the Cancer Society shared similar concerns about Permatan and warned against its use.
"This product has not been assessed for quality, safety or undergone rigorous tests for safety. Encouraging deliberate sun exposure or tanning bed use can increase risk of skin cancer, and is something we absolutely discourage."
Nat, who is a 10-year user of melantan products, had been using Permatan since November and said using the product was a waste of time.
She said the product gave her multiple side effects including nausea, flushing in the face and disturbed nasal cavities.
"So I was sneezing a lot, everyday at 6am I'd wake up sneezing and it would wake all my flatmates up too and then just having a runny nose and just feeling like it was going further up than just my nose, like into my head.
"I only used it once a day at night time because it also makes you feel sick. So you'd feel nausea ... I didn't throw up but yeah, I would feel quite sick.
"You get a really flushed face, and that's not pretty if you're going out in public," Nat said.
RNZ attempted to contact Permatan but the company had not replied to its questions at the time this story was published.
