Establishing an animal model for post-inflammatory hyperpigmentation following fractional CO2 laser application.

Background: Post-inflammatory hyperpigmentation (PIH) is a common cosmetic concern, often leading to significant psychological distress for the patients. With the widespread application of lasers including ablative fractional resurfacing (AFR) with a 10,600 nm CO₂ laser, PIH caused by lasers is becoming increasingly common. But due to the absence of an appropriate animal research model, our understanding of pathophysiological mechanisms and preventive strategies for PIH remains limited.

Methods: This study aimed to establish an animal model to investigate PIH following AFR CO₂ laser application, focusing on the dynamic changes in melanin, inflammatory cytokines, growth factors, and skin structures as PIH developed. We employed pigmented guinea pigs as our experimental subjects and conducted our research in two phases. In the first phase, we utilized three modes of AFR CO₂ laser to identify which laser mode could induce PIH by monitoring dynamic melanin changes. In the second phase, the laser mode that most reliably induced PIH was applied to re-establish the PIH model. Pathophysiological changes during PIH progression were investigated through histopathological observations, real-time quantitative polymerase chain reaction, and two-photon microscopy.

Results: We successfully established a replicable animal model for PIH following AFR CO₂ laser application. We observed a significant increase in inflammatory cytokines and growth factors within the skin tissue by the second week, with stable pigmentation becoming apparent by the third week.

Conclusions: Our research provides a promising animal model for understanding and further investigating the mechanisms of PIH after laser procedures.

Ebm level: V (animal study).