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, ten times more than did so five years ago. But for many people the process is prohibitively expensive, costing up to £1,300 for laser treatment and as much as £700 for professional bleaching. Professor Andrew Eder, clinical director of the London Tooth Whitening Centre, ...