If you yearn for a brighter smile, you might be considering one of the many tooth whitening kits available over the counter at drugstores and chain stores.

These products come in a variety of forms, including stick-on strips, dissolving strips and gels, and tooth-shaped trays that you fill with gel before placing on your teeth for a recommended period of time.

But will these tooth whitening products turn yellowing teeth whiter? And are they safe?

When They Work

Home tooth whitening treatments usually rely on the chemicals hydrogen peroxide or carbamide peroxide—which releases hydrogen peroxide—to bleach some of the discolorations that can build up over time in the outer layer of tooth enamel.

Lightening strips, gels, and gel-filled trays with one of those ingredients are typically used once or twice a day for up to 14 days.

These tooth whitening products can effectively lighten tooth stains caused by smoking and highly pigmented foods and drinks such as coffee, tea, cola, and red wine, according to Jay W. Friedman, D.D.S., M.P.H., a consumer healthcare advocate and dental adviser to Consumer Reports.

Most home tooth whitening products will leave teeth one to two shades whiter based on a 16-shade tooth bleaching scale when used as directed, according to a 2014 review published in the Journal of Evidence-Based Dental Practice.

“You will see a noticeable difference, but final results can vary depending on individual teeth and the depth of staining or discoloration,” says Edmond Hewlett , D.D.S., a professor of dentistry at the University of California Los Angeles and spokesperson for the American Dental Association.

The bonus for your wallet: Home tooth whitening kits cost a fraction of the hundreds of dollars you’d pay for whitening in a dentist’s office and may work just as well for some of the stains mentioned above.

When They Don’t

As good as home tooth whitening kits can be at tackling stains on the enamel that covers teeth, they are less effective against some other kinds of discoloration.

For example, tooth enamel normally thins with age, so dentin—the hard tissue under the enamel, which can be gray, brown, or blue in tone—may begin to show through.

A previous tooth injury or having taken the antibiotic tetracyline as a youngster can also lead to darkened dentin.

Both give teeth a darker look, which home tooth whitening kits can’t lighten, says Hewlett.

Stronger dentist-office tooth whitening procedures can sometimes lighten up dentin. “In-office whitening uses higher concentrations of the ingredients used in home kits,” he explains.

Keep in mind that both home tooth whitening and dentist-office whitening only work on natural teeth. So if you have caps, crowns, veneers, dentures, or white fillings, you’ll see no difference in those parts of your smile.

Safety and Side Effects

When used as directed, our experts say, home tooth whitening kits are safe.

But it’s worth checking in with your dentist first to rule out oral health issues that should be addressed. “Whitening with an unfilled cavity could be painful,” Hewlett notes.

In addition, be aware that home whitening can cause uncomfortable—but temporary—side effects.

“Some users develop gum irritation, especially if whitening strips or other products are in too much contact with gums,” says Hewlett. “And most people experience a little tooth sensitivity.”

For 10 to 15 percent of users, that sensitivity can be significant enough to cause them to discontinue whitening.

If you have sensitive teeth, before whitening, try brushing with a toothpaste for sensitive teeth starting a week or so beforehand. Continue to use that toothpaste throughout the home treatment.

If sensitivity occurs, consider skipping a day in between use of your home kit.

Avoiding extremely cold and hot foods and drinks during whitening can also keep you more comfortable.

And don’t use at-home kits more often than recommended. Doing otherwise can increase the likelihood of irritation and sensitivity.

Getting the Most From Home Tooth Whitening

Which type of home whitening product is most effective? It’s unclear.

A review of studies, published in the journal Clinical Oral Investigations, found products containing carbamide peroxide worked only slightly better at whitening than products containing hydrogen peroxide. (And see what our experts say about whitening toothpastes.)

When it comes to highly pigmented foods and drinks, be aware that in one study at least, cola caused even more staining in freshly whitened teeth than coffee.

“Cola should be avoided because it is an unhealthy drink—too much sugar,” Friedman says. “It stains the teeth and also causes erosion of the enamel due to its acidic content.”

Sipping iced tea and cold coffee drinks through a straw can help curb their discoloring effects.

So can swishing water around your mouth after a meal that contains foods and drinks that can affect tooth color.

And, of course, good dental hygiene is key. “Keep your teeth clean with regular brushing and flossing,” says Hewlett.