The nasolabial fold, also known as the "smile lines" or "laugh lines," is a natural facial feature that extends from the side of the nose to the corners of the mouth. It is a crease or fold that becomes more pronounced when a person smiles or laughs. The nasolabial fold is a normal part of facial anatomy and varies in prominence among individuals. Some people may develop deeper or more noticeable nasolabial folds due to factors such as ageing, genetics, skin elasticity, and facial expressions.