Tooth whitening kits have been found to contain illegally high levels of the bleaching agent hydrogen peroxide.
Trading Standards Institute (TSI) tests found hydrogen peroxide levels were higher than the legal limit in 18 out of 20 DIY products tested.
In one case the legal limit was exceeded by a factor of 230 times.
Hydrogen peroxide, commonly used as a hair dye, can aggravate gum disease and cause sensitive teeth - or even chemical burns to the mouth.
"We strongly recommend that anyone considering having their teeth whitened cosmetically should consult a qualified dentist"
It is thought that the use of tooth whitening kits is gaining in popularity, in part fuelled by a desire to replicate the dazzling smiles of Hollywood stars.
Ron Gainsford, TSI chief executive, said kits for home use cost as little as £14.
He said: "We strongly recommend that anyone considering having their teeth whitened cosmetically should consult a qualified dentist.
"However, I must stress that our tests were carried out on teeth whitening kits - and we are not suggesting there is a problem with the whitening toothpastes or polishes that are also on the market."
Only two passed
Officers from the Central England Trading Standards Authorities purchased 16 teeth whitening kits via the internet or over the counter from pharmacists or beauty shops across the Midlands.
They found that only two complied with the Cosmetic Products (Safety) Regulations, which ban the sale or use of teeth whitening products that contain more than 0.1% hydrogen peroxide.
The two that passed the test were Boots Expert Teeth Whitening Programme and the 'Brilliant' tooth whitening system, distributed in the UK by Brilliant Products, of Staines, Middlesex.
The remaining 14 contained amounts of hydrogen peroxide ranging from 0.24% to 23.8%.
In addition, Hertfordshire Trading Standards sampled four teeth whitening products, bought over the internet from UK suppliers.
They found all contained higher than the legal level of hydrogen peroxide, with one containing 7.3%.
Manufacturers and suppliers of all the items that did not comply with the 0.1% limit are now being contacted and advised to withdraw the products from sale.
Investigations are still going on with a view to possible further action.
A British Dental Association spokesperson said: "It is important any patient considering having their teeth whitened consults their dentist, who will examine their mouth properly, take a full medical history and discuss treatment options."
The BDA, through the European Council of Dentists, is involved in discussions to amend the EU Cosmetics Directive that will define the strength of products available to the public and remove restrictions on qualified dental practitioners using products of a higher strength.
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