Sleeping with your mouth open can make it as acidic as if you had just drunk a glass of orange juice, according to dental researchers who say this may promote decay and weakening of the teeth
The mouth's acidity level is typically neutral, with a pH of about 7.
Otago University post-graduate student Joanne Choi and colleagues experimented with 10 healthy volunteers by sometimes attaching a nose clip that made them breathe through their mouths.
The participants also had a small device clipped to their teeth to measure acidity and temperature and transmit the data to an external recorder.
Acidity increased slowly in everyone's mouths during sleep, but increased more over a longer period when participants were forced to mouth-breathe.