Q: Can whitening your teeth be harmful?

A: "No. Crest Whitestrips contain hydrogen peroxide, the same enamel-safe ingredient dentists use for tooth whitening and have been the subject of more than 100 clinical studies, all of which have shown them to be safe and effective," said Crystal Harrell, Oral Care External Relations Manager at Procter and Gamble.

She said Procter and Gamble has conducted safety studies in which people have used Crest Whitestrips twice a day for six months and saw no safety issues. Although some people may experience a mild degree of teeth and gum sensitivity, that is just temporary, she said.

The product works by keeping the whitening gel, which contains the hydrogen peroxide, onto teeth for 30 minutes at a time on thin, flexible strips. The 30 minutes is just long enough to get at stain build-up just below the surface. The whitening results can last anywhere from six to 18 months, she said.

The worst offenders of staining teeth are cola, juice, coffee, tea, wine and highly pigmented foods, such as beets and blueberries, Harrell said.

"If you cannot avoid them, tips include chewing crunchy foods after consumption, such as celery and carrots, or drinking staining liquids through a straw to avoid contact time with the teeth," she said.

Gillian Hay, president of the Pre-Dental Society at Penn State, said the at-home kit has one basic difference from a professional cleaning.

"The basic difference of using an at-home kit or going to a dentist to have your teeth whitened is that the at-home kits have similar chemical formulations at a lower concentration," Hay said. She said the take-home system is not as effective as whitening trays a dentist would make.

-Compiled by Cindy Hryszko