Split-Face Studies: When, Why, and How

In aesthetic dermatology, subtle differences matter. When a product is indicated in improving the appearance of a particular condition, it is important to use a study design that can detect subtle changes. One method that can be particularly useful in this context is the split-face study. At Maxeome, we believe in using the right study design for the right question. Here's what to know about split-face trials and when to use them.

What is a split-face study?

A split-face study is a type of clinical trial where two different treatments, or a treatment and a control, are applied to opposite sides of the same participant’s face. Each individual acts as their own control. This design allows researchers to compare the effects of the treatments directly, without interference from differences between individuals. Split-face studies are especially useful in aesthetic research because results are often based on visual outcomes, which can vary significantly from person to person. Using each participant as their own control helps reduce that variability and leads to more meaningful comparisons.

Split-face study schematic

Why use a split-face design?

There are several advantages to using a split-face design in aesthetic research. First, it reduces bias caused by individual differences. People vary widely in terms of skin type, age, sun exposure, and underlying skin conditions. By administering the intervention on one side (suppose it is the left side), and the control (right side), the study controls for these factors more effectively than traditional parallel-group designs.

Additionally, it increases the sensitivity of the study. Many aesthetic interventions produce subtle improvements. A split-face design allows researchers to detect those differences with fewer participants than would typically be required in a between-subjects study. Furthermore, this design can be more cost-effective. Because fewer participants are needed, recruitment, monitoring, and follow-up take less time and resources.

When is a split-face design not appropriate?

Although split-face studies offer many benefits, they are not suitable for every situation. Investigators should avoid this design when the treatment has systemic effects or one side of the face could unintentionally be affected by the treatment intended for the other side. It is also important to consider whether the study can be blinded. If the two treatments cause visibly different side effects, such as swelling or redness, blinding may not be possible. This could introduce bias in outcome assessments.

Finally, crossover effects may occur if inflammation or irritation spreads from one side of the face to the other. In such cases, the results would be difficult to interpret.

Designing a split-face study the right way

When using a split-face design, it is important to plan carefully to avoid common pitfalls. The side that receives each treatment should be randomly assigned. This prevents consistent bias from factors such as injection technique or the practitioner’s handedness. Standardized photography and validated rating scales should be used to measure outcomes objectively. Researchers should also document any baseline facial asymmetry, since differences in the natural structure of the face could influence the results.

In addition to clinical assessments, patient-reported outcomes are valuable. Patients may notice differences that clinicians overlook, especially in terms of comfort, satisfaction, or perceived improvement. Selecting endpoints that are specific to each side of the face, such as redness, pigmentation, or wrinkle depth, is also critical for accurate analysis.

Take-home message

Split-face studies are a valuable tool in clinical research when used appropriately. They allow for direct comparisons within the same individual, helping detect subtle treatment effects while reducing variability and cost. However, they are not suitable for all products or study goals. Careful planning, side randomization, and thoughtful outcome selection are key to producing reliable and clinically meaningful results.