By Dr. Edith Bracho-Sanchez, CNN

(CNN) -- Hydrogen peroxide, the active ingredient in over-the-counter whitening strips, may be harmful to the layer under the enamel of teeth, according to research presented Tuesday at a scientific meeting.

Teeth are made up of three layers: the outer enamel, an underlying dentin layer and connective tissue that binds it to the gum. The middle layer, dentin, is rich in proteins, of which collagen is the most abundant.

Most studies on the safety of hydrogen peroxide have focused on enamel. The chemical is known to penetrate the enamel and reach the dentin, although in miniscule amounts, explained Dr. Edmond Hewlett, associate dean at the UCLA School of Dentistry and spokesman for the American Dental Association, who was not involved in the new study.

Kelly Keenan, senior author of the study and associate professor of chemistry at Stockton University in New Jersey, said in a statement that she and her colleagues "sought to further characterize what the hydrogen peroxide was doing to collagen."

Essentially, all whitening products in the United States contain hydrogen peroxide and/or carbamide peroxide, according to the American Dental Association.

Using entire teeth and artificial saliva, the researchers watched the collagen in dentin break down into smaller proteins when treated with hydrogen peroxide, according to the results, presented at the American Society for Biochemistry and Molecular Biology meeting.

"Our results show that treatment with hydrogen peroxide concentrations similar to those found in whitening strips is enough to make the original collagen protein disappear," Keenan said.

Hewlett cautions against generalizing results obtained in extracted teeth, as they may not represent the same environment as a person's mouth.

Because the research is in its early stages, it's unknown to what extent the dentin is damaged, what this would mean for patients and whether the damage is permanent, he said.

"The tooth-whitening products that the abstracts are talking about have been around for decades and used by millions and millions of people," he said. "As far as the integrity of the tooth being damaged, that has not emerged."

The most common side effect that dentists see after the use of whitening strips is tooth sensitivity, which is transient and does not represent underlying damage of the tooth, he said.

Hewlett recommends looking for products that have the American Dental Association seal of acceptance, which means they have been tested for safety and effectiveness by the organization.