The literature includes numerous clinical trials to assess the effects of chlorhexidine varnishes in patients with chronic gingivitis and periodontitis. The purpose of this study is to review the literature systematically in order to ascertain the clinical effects of the different chlorhexidine varnishes at the periodontal level. The application of chlorhexidine varnishes seems to have beneficial effects in patients with chronic gingivitis, improving their plaque accumulation and bleeding levels and reducing their gingival index. It is possible to maintain this beneficial effect for prolonged periods of time, although this requires re-applications of the varnish. This review shows the need for new studies to assess these effects over the long term, in order to establish the number of applications and the interval between them that offer the best results over time.