What Condoms Cannot Cover: A Systematic Review of HPV, HSV, Syphilis, and Other Skin-to-Skin Sexually Transmitted Infections Despite Condom Use 

Background: Condoms are highly effective in reducing the transmission of many sexually transmitted infections (STIs); however, their protective effect against infections transmitted through skin-to-skin contact remains incomplete. Human papillomavirus (HPV), herpes simplex virus (HSV), and syphilis may still be transmitted despite correct and consistent condom use because infectious lesions or viral shedding can occur outside the condom-covered area.
Objective: This systematic review aimed to synthesize evidence regarding the acquisition of HPV, HSV, and syphilis among individuals reporting condom-protected sexual activity and to examine the residual risk associated with skin-to-skin transmission.
Methods: A systematic review was conducted according to PRISMA 2020 guidelines. Searches were performed in PubMed, Scopus, Web of Science, ERIC, and Google Scholar, supplemented by manual reference screening. Studies reporting STI acquisition despite condom use were included. Data were extracted and synthesized narratively because of methodological heterogeneity.
Results: A total of 473 records were identified, of which 13 studies met the inclusion criteria. The evidence consistently demonstrated that condoms reduce, but do not eliminate, the risk of HPV, HSV, and syphilis transmission. HPV infections persisted because of exposure to uncovered genital skin. HSV transmission occurred through asymptomatic viral shedding and lesions located outside condom-covered areas. Syphilis transmission remained possible through contact with infectious lesions on exposed skin or mucosal surfaces. Several studies also identified limitations associated with self-reported condom use.
Conclusion: Condoms remain an essential component of STI prevention but do not provide complete protection against skin-to-skin transmitted infections. Comprehensive prevention strategies, including vaccination, screening, sexual health education, and early treatment, should complement condom use.