It turns out skipping red wine isn't enough to keep your pearly whites bright. A new study from New York University pinpoints another indulgence that can turn teeth dingy - white wine. NPR's Patti Neighmond reports.

PATTI NEIGHMOND: It turns out the culprit in all wine that puts the stain into teeth is acid. Red wine is worse because it has a dark coloring that gives it a one, two punch, but the problem starts, says dentist Mark Wolff, with the acid.

Dr. MARK WOLFF (Dentist): The tart taste that we get out of the wine, that's actually an acidity.

NEIGHMOND: And that acidity actually erodes enamel on your teeth, etching in rough spots and grooves that then set the stage for intensely colored chemicals called chromogens.

Dr. WOLFF: The chromogen is a pigment. It's a very color-intense molecule. And it stays right on that tooth structure turning the tooth bluish-brown like a blueberry would.

NEIGHMOND: Or cherries would, or coffee or as in Wolff's study, black tea. Wolff used a couple of handfuls of cow teeth, which are similar to human teeth, only a lot bigger, so they're easier to work with.

Dr. WOLFF: We had three particular groups. We took all of these 18 teeth and we whitened them first just to make sure there was no stain on the surface.

NEIGHMOND: And then Wolff and colleagues submerged the first group of six teeth in water, then dunked them for several minutes in black tea - the result, no stain. Another group of teeth was submerged in red wine, then dunked in tea -the result, deep dark stains. No surprise. The rest of the teeth they submerged in white wine and then dunked in the tea.

Dr. WOLFF: We saw the tooth turn a very nice shade of brownish-red.

NEIGHMOND: It was the acid in the white wine that roughed up the teeth so they absorbed more of the pigment in the tea. Now, red wine still produced the darkest stains because it contains more pigment than white wine and more acid. Acidic erosion isn't just a problem with wines, though, says Wolff. Acid is also found in abundance in citrus drinks like grapefruit juice, lemonade, most sports and energy drinks and carbonated sodas. And that's part of the problem. People really like these acidic drinks. That's probably not a coincidence, says Marcia Pelchat. She's a scientist at the Monell Chemical Senses Center in Philadelphia, and she says people often view these acidic drinks as refreshing.

Dr. MARCIA PELCHAT (Scientist, Monell Chemical Senses Center, Philadelphia): Usually what people mean is that they alleviate thirst or remove some unpleasant coating from the mouth. Beverages that are refreshing tend to be acidic and carbonated.

NEIGHMOND: To help head off stains, Dr. Wolff suggests using a toothpaste with a whitening agent. But don't brush too hard and don't brush immediately after that wine or juice, or you could just make the problem worse - that's when tooth enamel is weakest. Patti Neighmond, NPR News.

BLOCK: Oh, and in case you were wondering, this was not an April Fool's joke.

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