Smile lines can refer to two different anatomical features of the face. First, the nasolabial folds which are the larger lines that extend from the nose to the corners of the mouth are often congenital but can deepen over time. Secondly, parallel to these lines near the lips are smaller lines that form from repeated movements over time. Both sets of these lines are commonly referred to as smile lines. So, with this in mind, why do smile lines get deeper?
The nasolabial folds deepen largely due to genetics and age. Some people will have nasolabial folds from childhood and as they get older, these will deepen. Movement of the face and cheeks does contribute, but less so than other lines on the face. Dermal fillers and sometimes Botox can lessen the appearance of these lines.
The smaller smile lines are usually formed by repetitive movements of the face and mouth. Like with other dynamic wrinkles and movement formed wrinkles, they take time to develop and are often subtle at first. Botox can be used to treat these, however, it does come with a higher risk of paralyzing certain important muscles that contribute to lip movement. Therefore, it is not commonly performed.