When does it get too much?

It depends on how healthy your mouth is and your eating habits (such as drinking coffee, red wine, etc.). Teeth whitening is preferred every 6 months to 12-18 months. It is preferable not to do more than that, as the peroxide in whitening products may damage the teeth and cause increased sensitivity, as well as gingivitis. The whitening strips also scrape the outer layer of the teeth, which is known as the enamel layer.