Some products available on the high street were found to reduce the hardness of enamel, according to early findings published in the British Dental Journal.
Consumers have been urged by the British Dental Association (BDA) to exercise caution and not gamble with the health of their smiles.
Five non-hydrogen peroxide whitening products from Boots and Superdrug were tested as part of the study.
The researchers found three of the products had an active ingredient of sodium chlorite, which they said reduced the hardness of teeth when acid was present.
It also increased the chances of future surface abrasions.
“Not all bleaching products are the same and not all bleaching products are safe,” lead author Dr Joseph Greenwall-Cohen, from the University of Manchester Dental School, said.
“It is essential that the public realise this and undertake more caution in selecting the bleaching or whitening products they apply to their teeth.”
The BDA also warned that many over the counter products containing hydrogen peroxide, used by dentists to whiten teeth, are ineffective.
It is illegal for the amount of hydrogen peroxide to be above 0.1%, but the BDA said it is too weak at this level to make a difference.
Professor Damien Walmsley, the BDA’s scientific adviser, said: “At best, people may be wasting their money buying over the counter and online products to whiten teeth.
“Home whitening kits are likely to take longer and be less effective than treatment from the dentist.
“While hydrogen peroxide, as used in dental practices, is the gold standard for whitening teeth, the lack of clarity over chemicals used in over the counter and online products means you could be gambling with your teeth.”
The British Dental Bleaching Association said: “We are concerned that the over the counter products included in the study may be harmful to teeth and advise the general public to see their dentist if they are considering having their teeth whitened.”
