How reliable is saliva testing?

Saliva testing can be useful in forensic investigations, but it is not definitive and must be interpreted carefully.

The most commonly used screening methods include the Phadebas test and RSID-Saliva. These tests detect biological markers associated with saliva, rather than identifying saliva itself.

Importantly, these markers are not exclusive to saliva. Phadebas and RSID-Saliva have been shown to react with other forensically significant biological materials, including vaginal secretions, faeces, and urine. A positive result therefore indicates that substances consistent with saliva may be present, not that saliva was definitively deposited.

DNA may sometimes be recovered from areas where saliva is suspected, but the presence of DNA does not confirm that saliva was the source. DNA can originate from skin cells, transfer during handling, or prior contact.

Environmental exposure, surface type, washing, and time can all influence whether saliva-related markers or DNA are detected.