Forensic Reliability of Body Fluids in Sexual Assault Investigations: A Systematic Review

The forensic reliability of biological fluids in sexual assault investigations depends on substrate type, environmental exposure, time since deposition, and analytical methodology. This systematic review evaluates the forensic reliability of major biological fluids, semen, blood, saliva, and vaginal secretions by comparing detectability and persistence on porous and non-porous substrates, assessing environmental and temporal effects on DNA integrity, and examining the performance of identification methods. A systematic search of PubMed, Scopus, and Web of Science (2001–2025) was conducted following PRISMA 2020 guidelines. Eligible studies investigated fluid persistence, degradation, or identification reliability under controlled or casework-relevant conditions. A weighted scoring framework categorised relative reliability. Twenty-seven studies met inclusion criteria. Semen and blood demonstrated higher reliability across substrates, particularly when collected within recommended timeframes. Porous substrates reduced surface detectability but occasionally preserved DNA from rapid degradation. Elevated temperature, humidity, and prolonged intervals consistently reduced DNA quality and detection success. Molecular approaches, including mRNA profiling, showed enhanced specificity in degraded or mixed samples, though methodological variability limited direct comparability across studies. The forensic reliability of biological fluids is context-dependent, shaped by complex interactions between substrate characteristics, environmental exposure, and analytical technique. Semen and blood remain robust DNA sources, while emerging technologies offer improved specificity in challenging scenarios. Standardised evaluation frameworks and timely evidence collection remain essential to enhance evidential value and minimise misinterpretation in sexual assault investigations.