Young women are jeopardising their health by using DIY teeth-whitening treatments involving baking soda, ash and hydrogen peroxide, say scientists.
A growing number of websites are promoting at-home techniques, which can cause permanent damage to tooth enamel and gums.
Dentists warn that some of the DIY treatments can dissolve the enamel of the teeth so they actually look darker in colour.
The popularity of teeth-whitening has increased tenfold in the past five years and at least 100,000 people have some form of treatment every year.
There are also cheaper whitening gels and 'deep clean' tooth brushes available from pharmacists for up to 100 pounds, although these are not deemed to be effective.
"There seems to be a growing concern among teens about their teeth, and the internet offers many whitening recipes. Some of these have the potential to damage healthy teeth," the Daily Mail quoted Anthony Eder, clinical director of the London Tooth Wear Centre, as saying.
"Household baking soda is an abrasive, so that with repeated use the white enamel may be worn away and leave teeth browner and with increased sensitivity. Salt crystals will scratch the enamel. Any treatment involving acid is particularly harmful," he added.
Stuart Johnston of the British Dental Association said that trying to use recipes for whitening from the internet really isn't a good idea and could lead to individuals damaging their teeth and causing themselves pain.