Even if you haven’t done much research into maintaining your oral health, you’re probably familiar with how cavities look and feel. Statistically, most people will have one at some point in their life—according to the National Institute of Dental and Craniofacial Research, 90% of adults 20-64 have experiences tooth decay at some point.

Many people may not be aware that cavities can also form in between their teeth. These “interproximal” cavities can be hard to spot, even if you know what to look for. If you’re worried you might be suffering from one, or if you just want to be vigilant, here’s how you can tell that there’s decay in between your teeth.