Rehydrating sports drinks are up to 30 times more erosive to teeth than water, according to researchers at the University of Birmingham.
Fizzy drinks can cause similar problems, the researchers warn
They found the drinks can dissolve tooth enamel and the hard dentine underneath, exposing the pulp.
Researchers said sports drinks had high acidity levels designed to increase their shelf life.
They found that athletes' dry mouths meant that they did not produce enough saliva to regulate the acidity.
The study involved a group of active participants who wore mouth protectors to protect their own teeth, with enamel samples mounted into the gum shield.
Dr Asker Jeukendrup, who was part of the research team, said: "There's two reasons why athletes are more at risk.
"The first is that when they exercise their saliva production is reduced.
"They get a drier mouth and that increases erosion.
"The second reason is that because athletes sweat a lot they lose a lot of fluid and they have to replenish that fluid, so they drink more than most people."
The reasearch team have used low-erosion technology to produce a sports drink which is less harmful to teeth.
Dr Tony Smith, head of research at the University of Birmingham's School of Dentistry said: "This study has shown that whilst an existing sports drink was erosive, it has been possible to formulate this new sports drink with negligible erosive potential.
"It's also important to remember that similar erosive problems can occur when drinking fruit juices or fizzy drinks."