Self-treatments using baking soda, ash and hydrogen peroxide, many of which are detailed online by members of the public with no dental experience, can strip tooth enamel and cause lasting damage to the gums, experts cautioned.
The techniques are becoming an increasingly popular alternative to expensive professional treatment, especially among teenage girls.
Examples of the potentially hazardous advice offered online include brushing the teeth with soap, salt, baking soda and hydrogen peroxide or bleach.
But dentists said some of the methods can erode the enamel covering of the teeth, making them appear darker rather than whiter.
Up to 100,000 people undergo some type of teeth whitening treatment each year, 10 times more than did so five years ago.
But for many people the process is prohibitively expensive, costing around $2,000 for laser treatment and possibly more than $1,000 for professional bleaching.
Professor Anthony Eder, clinical director of the London Tooth Whitening Centre, told the Daily Mail: “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.”
He said using baking soda repeatedly would strip the teeth of enamel, leaving them browner and more sensitive, while salt would scratch the enamel and any use of acid was especially damaging.