Background <p>Polyacrylamide hydrogel (PAHG) is a new biomaterial that emerged in the last century and has been widely used in human filler procedures, such as injectable breast augmentation and facial contour improvement. However, as the implantation time of the material increases, various complications have been reported, which reflects that the safety of this material has not been adequately studied. Therefore, a more in-depth experimental analysis becomes particularly important.</p> Methods <p>We collected lesion tissues from six patients with PAHG facial injection. The lesion tissues were examined histologically and molecularly.</p> Results <p>Complications caused by PAHG facial injection included pain, subcutaneous nodules, swelling and gel displacement. Western blot revealed decreased expression of neural tissue markers, and increased expression of macrophage markers and oxidative stress-related factors. The results of this study provide new insights into the mechanism and development of PAHG facial injection complications.</p> Conclusion <p>This report explores the possible mechanism of PAHG complications after facial injection from a new perspective of oxidative stress and inflammation for the first time, which provides a reference for researchers and clinicians to further understand the characteristics of materials and strictly control surgical indications to reduce complications.</p> No Level Assigned <p>This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors <a href="http://www.springer.com/00266">www.springer.com/00266</a>.</p>