Celebrities like Gwyneth Paltrow and Jennifer Aniston reportedly start their morning with a glass of warm lemon water for health purposes, according to True Lemon, but dental experts say, this habit is actually ruining their smiles.

"Lemon juice is a popular drink in the morning, but unfortunately it is highly acidic (with a pH between 2 and 3) and therefore can contribute to enamel erosion or tooth wear over time," says an expert from the British Dental Association, according to Huffington Post U.K.

Adding sugar into the drink is worse. "Lemon juice can cause erosion and sugar increases the risk of tooth decay," the expert added.

But Dr. Christine Skordelese, a cosmetic and biomimetic dentist, told Marie Claire, "As long as you're not sucking on lemons all day long, having fresh lemon water is good for you. It actually helps prevent disease."

She did agree that it can strip the enamel off over time, but said that lemon water is better than drinking coffee with milk, which can lead to cavities. She also said that an actual lemon fruit is better than bottled lemon juice.

Drinking lemon water is better after you've brushed your teeth, according to The Smile Center. Waiting at least two hours before cleaning your teeth again will also give the saliva time to "remineralize" the teeth.

Meanwhile, strawberries, another healthy food that was originally thought to help whiten and brighten teeth when mixed with baking soda, doesn't actually have any bleaching benefits. "The only benefit of the do-it-yourself method - strawberries and baking soda - is, while it seems to make your teeth look whiter, they look whiter because you're just removing plaque accumulation on your teeth," said So Ran Kwon, who researched teeth whitening, according to Live Science.

Apples also work to the contrary, despite notion that its fiber can help neutralize acids in the mouth. "Apples have a high acidity content and one of the things we are concerned about is erosion," said the British Dental Association, according to Daily Mail. "Research shows that dental erosion in adults due to diet is usually a result of excessive consumption of fruits and fruit juices," the spokesperson added.