Abstract Background Fat grafting is a popular operative approach for rejuvenation. Some patients requiring facial fat grafting also have acne. Fat grafting may improve acne in some patients. Objectives The aim of this study was to assess whether fat grafting can improve acne and to analyze the mechanism of action by which such improvement occurs. Methods Preoperative and postoperative digital photographs were examined retrospectively in 229 patients who underwent fat grafting to compare the numbers of inflammatory acne lesions. In addition, 18 patients with acne who were treated by injection of subdermal stromal vascular fraction gel (SVF-gel) were examined prospectively. The numbers of inflammatory acne lesions before and after treatment were measured, and changes in the levels of CD4+ T-cell infiltration were determined from immunohistochemical staining. Results Of the 229 retrospectively evaluated patients who underwent fat grafting, 22 had acne and had complete follow-up data; in these patients, the numbers of acne lesions were significantly lower after than before treatment. The 18 patients who received subdermal SVF-gel injection showed evident improvements in inflammatory lesions after more than 1 year of follow-up. CD4+ T-cell infiltration was significantly decreased at week 4. Conclusions Facial fat grafting can improve inflammatory acne lesions, perhaps because adipose-derived stem cells, which are plentiful in SVF-gel, reduce CD4+ T-cell-mediated inflammation responses. Level of Evidence: 4