Reports of illegal teeth-whitening that could leave patients at risk of health problems including burns or lost teeth have increased.
General Dental Council (GDC) figures showed a 26% rise in reports last year.
Teeth-whitening can only be performed legally in the UK by professionals registered with the GDC.
One beauty school claimed to have provided “thousands” of candidates with illegitimate qualifications, an undercover investigation found.
Failure to comply with the requirement to be registered can result in a criminal record and an unlimited fine.
Untrained beauticians using teeth-whitening kits have been known to cause tooth loss, burns and blisters.
Dr Ben Atkins, president of the Oral Health Foundation, said: “When things go wrong in dentistry, they can really go wrong.
“I’ve been that dentist with the full back up service when the patient’s had that heart attack.
“It would be catastrophic for the patient and the person who’s been trained and told it’s legal to do it.”
Last year 732 cases of illegal-teeth whitening were reported to the GDC, a 26% increase from 582 in 2018 – though the figure was higher in 2016.
The dentists’ regulatory body relies on reports from customers, so the real number could be much higher.
The GDC said it had launched 126 prosecutions against illegal teeth whiteners since 2015.