BACKGROUND: Surgical site infections are a continuing concern in health care. Microbial sealant is a liquid applied to the skin immediately before surgery. It is thought to contribute to reducing surgical site infections by sealing in the skin flora to prevent contamination and infection of the surgical site. OBJECTIVES: To assess the effects of the preoperative application of microbial sealants (compared with no microbial sealant) on the rates of surgical site infection in people undergoing clean surgery. SEARCH STRATEGY: We searched the Cochrane Wounds Group Specialised Register (searched 10 May 2010), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 2), Ovid MEDLINE (1950 to April Week 3 2010), Ovid MEDLINE - In-Process and Other Non-Indexed Citations (searched 10 May 2010), Ovid EMBASE (1980 to 2010 Week 18) and EBSCO CINAHL (1982 to 10 May 2010). We searched bibliographies and contacted manufacturers of microbial sealants for unpublished studies. There were no restrictions based on language, date or publication status. SELECTION CRITERIA: Randomised controlled trials (RCTs) were eligible for inclusion if they involved people undergoing clean surgery in an operating theatre and compared the use of preoperative microbial sealants with no microbial sealant. DATA COLLECTION AND ANALYSIS: All review authors independently extracted data on the characteristics, risk of bias and outcomes of the eligible trial. MAIN RESULTS: One small trial (177 participants undergoing hernia repair) met the inclusion criteria. There was no statistically significant difference in the rates of surgical site infection (three patients in the control group developed a surgical site infection compared with none in the intervention group; risk ratio (RR) 0.17, 95% CI 0.01 to 3.19, P = 0.23).