Background: Injectable dermal fillers became more popular for improving skin contour defects such as wrinkles, lines, and depressed acne scars.  Aim of the work: This work aimed to study different skin changes induced by dermal filler injection in adult and aged albino rat.  Material and Methods: Forty five female albino rats were used. The animals were divided into three groups: Group I (Control): Included twenty adult rats. Group ІІ: Included fifteen adult rats, they received an injection of 0.1 ml of hyaluronic acid (HA). The animals were subdivided into three subgroups according to time of sacrification , five rats each: Subgroup IIa: after 7 days. Subgroup IIb: after 60 days. Subgroup IIc: after 90 days. Group ІІІ: Included ten aged rats, they were subdivided into two subgroups, five rats each: Subgroup IIIa: (Control aged group). Subgroup IIIb: the rats were given an injection of HA and were sacrificed after 30 days.
Results:Thin skin of HA injected animals revealed significant (< 0.05) increase in the thickness of subcutaneous tissue (SC) and significant increase in collagen and elastic fibers, and significant increase in the CD34 positive endothelial cells as compared to control and aged rats. Active fibroblasts at the site of injection showing euchromatic nuclei. Their cytoplasm contained well developed rER, numerous mitochondria, many vesicles, and centrioles.
Conclusion: Hyaluronic acid filler injection stimulated vascularization and enhanced fibroblasts to synthesize collgen and elastic fibers in SC. This protected the skin from aging features in adults,and play a role in improvement of skin defects in aged rats.