Saliva as evidence

DEFINITION: Complex fluid mixture secreted from the salivary glands into the mouth or oral cavity.

SIGNIFICANCE: Saliva is an extremely useful tool in many forensic applications, in part because the collection of saliva samples is relatively simple and noninvasive. Even small samples of saliva will yield the donor's blood type as well as DNA for comparative purposes.

Saliva contains water, electrolytes, mucus (consisting of mucopolysaccharides and glycoproteins), various enzymes, and opiorphin, a pain-killing substance. Saliva has many functions in the human body. It aids digestion by moistening food and binding it together so that it may be more effectively chewed. It also lubricates food, permitting swallowing and easy passage of food down the esophagus, thereby minimizing irritation of the lining of the oral cavity. The salivary enzyme amylase initiates the digestion of carbohydrates such as starch, and the addition of saliva enables food and liquid molecules to more readily interact with the taste buds on the tongue, thus enhancing taste.

Saliva aids oral hygiene by flushing food debris from the mouth. It contains the enzyme lysozyme, which destroys many bacteria, thereby acting as a disinfectant; however, many pathogenic bacteria can thrive in the mouths of humans and other animals. Saliva also functions as a protective barrier, as when nausea reflexively triggers saliva flow, which coats the oral lining and teeth before vomiting occurs, so that acidity is minimized.

The amount and type of saliva secretion are controlled by the autonomic nervous system. Increased stimulation leads to increased blood flow to the salivary glands, which stimulates the production and release of saliva. Sympathetic stimulation results in an increased amount of mucus in the saliva, and parasympathetic stimulation results in increased volume of watery saliva production (serous saliva).

Saliva samples are often important in criminal investigations. Collection of saliva is relatively simple and noninvasive, and only a small amount is needed for the determination of an individual’s blood type and for the extraction of DNA (deoxyribonucleic acid) for comparisons. Saliva can also reveal the drugs an individual has taken; in some cases, exposure to certain drugs can be detected through analysis of saliva.

Saliva samples also permit evaluation of general health, and saliva tests have been developed for the detection of certain medical ailments, such as human immunodeficiency virus (HIV), and other health problems. Saliva samples that reveal the presence of viral, bacterial, or systemic diseases may link their donors to crime scenes or to objects. Furthermore, the presence of certain bacteria not identified with other bodily fluids can help investigators determine that fluid samples are saliva.

Saliva may be tested using various methods. Generally, these tests are classified as destructive or non-destructive. Non-destructive methods preserve the integrity of evidence, which can then be used for further processing, such as DNA profiling or saved.

Bibliography

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Li, Richard. Forensic Biology. 2nd ed., CRC Press, 2015.

Mandel, Irwin D. “The Diagnostic Uses of Saliva.” Journal of Oral Pathology and Medicine, vol. 19, no. 3, 1990, pp. 119–25, doi:10.1111/j.1600-0714.1990.tb00809.x. Accessed 27 Feb. 2026.

McClintock, J. Thomas. Forensic Analysis of Biological Evidence: A Laboratory Guide for Serological and DNA Typing. CRC Press, 2014.

Su, Chih-Wen, et al. “Saliva Identification by RT-LAMP Integrated with CRISPR-Cas and LFA.” Forensic Science, Medicine and Pathology, vol. 21, 2025, pp. 1720–29, doi:10.1007/s12024-025-01079-4. Accessed 27 Feb. 2026.

Sweet, D., and D. Hildebrand. “Saliva from Cheese Bite Yields DNA Profile of Burglar: A Case Report.” International Journal of Legal Medicine, vol. 112, no. 3, 1999, pp. 201–3, doi:10.1007/s004140050234. Accessed 27 Feb. 2026.

Upadhyay, Megha, et al. “Recent Advancements in Identification and Detection of Saliva as Forensic Evidence: A Review.” Egyptian Journal of Forensic Sciences, vol. 13, 14 Mar. 2023, doi:10.1186/s41935-023-00336-3. Accessed 27 Feb. 2026.

Walsh, D. J., et al. “Isolation of Deoxyribonucleic Acid (DNA) from Saliva and Forensic Science Samples Containing Saliva.” Journal of Forensic Sciences, vol. 37, no. 2, Mar. 1992, pp. 387–95, doi:10.1520/JFS13248J. Accessed 27 Feb. 2026.