Add tea to your milk in your tea stops your teeth being stained, researchers have found.
A protein in the milk prevents tannins in the tea discolouring the enamel.
It is said to be even more effective than whitening toothpastes and as good as some bleaching products.
"Tea is the second most consumed drink in the world, and the way it's processed affects how teeth are stained," said Dr Ava Chow, who led the Canadian study.
"The more the tea is processed or oxidized, the higher its staining properties are. But we've found that the addition of milk to tea reduces the tea's ability to stain teeth."
Tea contains tannins - water soluble compounds that cause the bitter flavour. They are dark in colour and can stain the teeth. The study found that casein, the main protein in milk, binds to the tannins in tea and prevents staining. Dr Chow, from the University of Alberta's School of Dentistry, initially designed her study as a way of introducing undergraduate dental hygiene students to research.
She was so surprised by the results she decided to publish them.
As part of the study, Dr Chow used human teeth that had been extracted, excluding teeth that had fillings, signs of tooth decay, or obvious cracks and fractures. She analysed the colour of the teeth and recorded them, before putting them through a "staining process".
This involved putting the teeth into either a solution of tea, or a solution of tea with milk at body temperature - 37C. After 24 hours, she recorded the colour of the teeth again.
"The results we found showed that casein is the component of milk that is responsible for the reduction of tea-induced staining," Dr Chow said.
"The magnitude of the colour change observed in our experiments is comparable to the colour change seen by vital bleaching products and more effective than whitening toothpastes."
Dr Chow said that before dentists advise their patients to take milk with their tea, they should consider whether milk-drinking is part of the person's culture.
"Adding milk to tea is a culture-specific phenomenon," she said.
"Some cultures may refuse to add it and others only drink tea with milk."
The research was published in the journal International Journal of Dental Hygiene.
- Daily Mail