Whilst blood and semen are the two most commonly encountered body fluids, saliva can often arise as a significant forensic evidence type, for example:
- on a mask worn during a robbery can help to identify the offender
- drinking vessels or cigarette ends at scenes of crime
- genital swabs in a sexual offence
- upper areas of clothing where it can help identify the wearer of the garment
However difficulties occur because saliva cannot be easily identified. The test to identify whether it is present relies on the detection of a substance called amylase which is usually present in large amounts in saliva. Complications arise because amylase also exists in other body fluids although with the exception of faeces and vaginal secretions it is usually present at much lower levels than in saliva.