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You may seek to dazzle with your grin . . . but whitening your teeth could be putting you at risk.

Experts have discovered that 18 out of 20 whitening kits tested contain illegal levels of bleach.

One product they looked at contained 230 times the legal level of hydrogen peroxide, the common active ingredient.

The chemical, which can be used to dye hair blonde, could cause serious burning to the mouth.

The findings were revealed by the Trading Standards Institute yesterday at its annual conference.

Manufacturers and suppliers of those kits which did not meet the legal limit of 0.1 percent for hydrogen peroxide, are being advised to withdraw them for sale and could face prosecution.

However, the unsafe brands have not been named.

Chief executive Ron Gainsford said: "Hydrogen peroxide is a chemical well known in the hairdressing industry, but it is also used in teeth whitening products to bleach teeth.

"Many people these days aspire to having the perfect Hollywood smile and some stars have paid a lot of money to achieve this through cosmetic dental treatment.

"There are much cheaper kits on sale for home use. But this could end up burning more than a hole in your pocket.

"We strongly recommend that anyone considering having their teeth whitened cosmetically should consult a qualified dentist."

In the last five years, the desire for cosmetic dentistry has increased.

But as well as causing chemical burns to the mouth, high levels of the bleach can aggravate gum disease and cause sensitive teeth.

The institution only tested tooth whitening kits. It did not look at whitening toothpastes or polishes on the market. For the research, officers from Trading Standards in Central England bought 16 teeth whitening kits on the Internet or over the counter from pharmacists or beauty shops across the Midlands.

Just two complied with the Cosmetic Products (Safety) Regulations.

They were the Boots Expert Teeth Whitening Program and the "Brilliant" tooth whitening system, which is distributed in the UK by Brilliant Products, of Staines, Middlesex. The remaining 14 contained between 0.24 percent and 23.8 percent of hydrogen peroxide.

The four other whitening products were sampled by Hertfordshire Trading Standards.

Officers bought them on the Internet from UK suppliers.

All contained higher than the legal level of hydrogen peroxide, the highest being 7.3 percent.

Operations manager Mike MacGregor said: "We support the limit of 0.1 percent hydrogen peroxide for products used by anyone who is not a qualified dentist."

There may be scope to allow dentists to use higher concentrations of the bleach, he said. Currently, they would be breaking the law by using such products.

Those using whitening kits are generally advised to squirt a line of cream into a mould.

Then they are told to bite down on the mould, which fits over the teeth, for a set period - usually several minutes.

Quite often, repeated treatments are recommended over days and weeks to get the desired smile.

The Institute did not name the dangerous brands as it is considering prosecutions and does not want to prejudice the cases.

However, it warned that many of the suspect DIY products are sold by beauty parlors and spas as well as retail outlets and over the Internet.

Some of the brands say that they contain more than 0.1 percent hydrogen peroxide in the list of ingredients, it added.

These products will have been produced for foreign markets where the health controls are less stringent, it said.

The institute advised those who have bought kits to go back to the retailer and ask how much hydrogen peroxide they contain.

(China Daily June 29, 2007)