The Ideal Lips: Lessons Learnt from the Literature.

Defining the ideal dimensions and proportions of the human face has been attempted for centuries, popularised in the Renaissance period by artists including Leonardo Da Vinci. The lips are part of the lower third of the face and are central to lower face aesthetics and the overall symmetry of the face. They also place an important part in conveying facial emotions and expressions. Full lips with well-defined Cupid's bow have always been associated with youth and beauty. The approval of hyaluronic acid use for tissue augmentation and the prevalence of social media have caused an exponential increase in lip augmentation procedures (Linkov et al. in Arch Plast Surg 46(3):248-254, 2019), as such researchers and aestheticians have focused on characterising the ideal lips mathematically to help guide clinicians. This narrative review will summarise the available evidence in the literature pertaining to the ideal lips, taking into account age, ethnicity and gender differences. LEVEL OF EVIDENCE III: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .