Some tooth whitening products bought from online marketplaces such as eBay, Amazon Marketplace and Wish could damage your teeth, a new investigation warns.

The consumer watchdog Which? tested the ingredients of 36 teeth whitening products available on a range of online marketplaces, including whitening strips, gel-filled syringes and pens with brush tips. 

Worryingly, 21 of the 36 teeth whiteners exceeded the legal amount of hydrogen peroxide permitted for home use, putting users at risk of burnt gums and permanent damage to teeth. 

Teeth whitening products sold over the counter should legally only contain up 0.1% hydrogen peroxide, while the legal limit for application by professional dentists is 6%. However, many of the products tested exceeded these levels by a significant margin.

Six of the most potent teeth whiteners had more than 100 times too much hydrogen peroxide to be legally sold. Five of these products were purchased from AliExpress. One ‘teeth bleaching gel kit’ contained 30.7% hydrogen peroxide. 

Five out of nine of the products tested from eBay broke the law on hydrogen peroxide levels – the worst offender contained 7.43%. Meanwhile five out of 13 of the products tested on Amazon Marketplace had illegal amounts of hydrogen peroxide, with one pen containing 7.87% of the chemical. 

The investigation also found evidence of teeth whitening products available elsewhere in the world – but illegal in the UK – being sold to British consumers.

The researchers found Crest Whitestrips being sold through a China-based Wish seller willing to ship to the UK. In lab tests, the strips were found to contain more than 132 times the legal amount of hydrogen peroxide in the UK.

Procter & Gamble, owner of the Crest brand, told Which? that it doesn’t sell this product in the UK or Europe, as the law doesn’t permit its sale there. 

The British Dental Association (BDA) recommends consumers visit their dentist for teeth whitening.  

“Hydrogen peroxide is a seriously strong chemical and not to be messed with,” BDA board member Paul Woodhouse tells HuffPost UK. 

“Dentists are trained in its usage and to consider a patient’s wider health and detect problems, such as gum disease for example, that may impact on the suitability of an individual to have their teeth whitened. They also know what whitening products are effective to use, and safe for teeth and gums.”

Due to legal restrictions on hydrogen peroxide, manufacturers of some at-home products use chemicals other than hydrogen peroxide, such as sodium perborate and chlorine dioxide, to whiten teeth, he adds, flagging that these come with “serious safety concerns” and shouldn’t be used.

“Using DIY measures that involve unspecified chemicals, or dangerously high levels of hydrogen peroxide is an avoidable and wholly unnecessary risk,” Woodhouse says. “This self- inflicted damage from could result in burnt gums and weakened teeth – and may need expensive root canal treatment to repair the damage.”