BackgroundSkin aging as a continuous and irreversible process is mainly the result of alterations of function and structure of the dermis. Among the modalities used for treating skin aging, carboxytherapy has been introduced as a safe minimally-invasive method for rejuvenation, reparation, and reconditioning of the skin.ObjectiveWe assessed the efficacy of carboxytherapy for the treatment of intrinsic skin aging through pathological and immunohistochemical (IHC) investigations.MethodsOur study was a split-body, randomized clinical trial on 15 female patients with intrinsic skin aging of the abdomen. Carboxytherapy was performed on one side of the abdomen, weekly for 10 sessions, while the other side was left untreated. Two weeks after the last session, skin biopsies were taken from both sides of the abdomen. Staining with hematoxylin-eosin, Masson-trichrome, and Orcein Giemsa was performed for the assessment of epidermal and dermal thickness, collagen, and elastin organization, respectively. IHC examination was performed for investigation of TGF-β1 and VEGF.ResultsPathological examination showed a significant increase in epidermal and dermal thickness and re-organization of collagens and elastic fibers with carboxytherapy. IHC examinations revealed a significantly increased expression of TGF-β1 and VEGF with carboxytherapy.ConclusionOur study demonstrated the effectiveness of carboxytherapy in treating and reversing intrinsic aging skin through pathological and IHC studies.