A Safe and Effective Lip Augmentation Method: The Step-by-Step Φ (Phi) Technique

Background: The shape and fullness of the lips are essential in facial aesthetics. We describe a safe injection technique of hyaluronic acid (HA), based on the well-known golden number Phi (phi), for lip augmentation. Methods: The name given to that procedure is "the step-by-step Phi technique." Firstly, "step-by-step" because we never inject more than 1-1.5 ml of HA in 1 session, and "phi" because we apply the golden ratio 1.618-broadly known as Phi-to identify the proper points for injection. Using a specific caliper, we identified 3-4 points in each upper half of the lip. We injected 0.01-0.05 ml of lower concentration (25 mg/g) HA in these particular areas of the upper lip, from the vermillion border into the vermillion. We took into consideration the existing lip volume to decide the proper amount of HA to be injected in every single site, as lips are often asymmetric. On the lower lip, we use the same caliper to identify again the proper injection points. If necessary, the next 2 sessions are performed at an interval of 15-30 days. Results: Our technique was performed in 833 patients. Mean age was 30.2 years (range: 18-72 years), and most patients were very satisfied. With this technique, we avoid severe complications such as arterial embolism or venous occlusion and unnatural results. The most common side effects were swelling, redness, and mild pain. Conclusion: The step-by-step Phi technique is safe, easy to learn and perform, and can provide natural results in lip augmentation.