Asked by: Ryan Hammond, US
Your skin isn’t completely flexible and collagen fibres can get microscopic tears when they are folded or stretched. Mostly your body will repair this damage but sometimes the new collagen fibres will be too long and your skin will get a little baggier. Or they might be too short and pinch the skin slightly.
Over time, these botched repairs accumulate at points where our face is frequently creased, such as the laughter lines round the eyes.
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.