Asked by: Lewis Pollard, Leeds

The main cause is gum disease. A 2010 study found that 47 per cent of Americans over 30 had some degree of gum disease. The bacteria attack the bone tissue in your jaw just behind the gum and cause it to slowly erode. Without healthy bone tissue to act as a scaffold, the gums first peel away from the tooth and eventually shrink back. Regular toothbrushing and flossing can fight gum infection but overbrushing damages gums too.

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.


luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.