Influencers posting dental advice

When used in large quantities, hydrogen peroxide can be harmful -- particularly if applied to cavities or diseased gums. 

Before whitening, dentists clean teeth to remove any surface discolouration, a process which does not happen for at-home products bought online.

Dental surgeon Lequart said that using too much of these products can cause irritation or even lead gums to recede -- an early warning sign of future tooth loss.

One online customer said the Crest strips "lighten teeth several shades, of course, but give a horrible sensation during hot or cold meals".

Lequart said that "on social networks, the target audience is relatively young and concerned about savings".

This could lead to a potential "disaster in terms of oral health", he added.

Wagner emphasised that most young people have perfectly healthy teeth and should not use "whitening products, which damage their teeth prematurely via acids".

Lequart cautioned that before-and-after whitening images on social media are often touched up using Photoshop.

And Couchat pointed out that influencers promoting these products often have expensive porcelain veneers covering their original teeth.

"They are taking advantage of people's credulity. It's a big scam," he added.

These veneers are also popular among Hollywood stars, a common inspiration for many dreaming of a whiter smile.