Hock a loogie and you’ll see it — that slimy, bubbly, lovely liquid known as spit.

A complex fluid known in more refined circles as saliva, the initial benefits of spit may seem obvious. Spit lubricates our esophagus and binds to our food, allowing us to participate in the joy of eating. The flow of saliva flushes out populations of bacteria in the mouth, keeping up our oral hygiene. But spit is also considered a game-changer when it comes to athletics, psychology, medicine, and crime.

But what is spit? Produced and secreted from salivary glands, saliva is secreted from clusters of cells called acini: a mixture of water, electrolytes, mucus, hormones and enzymes. When spit moves through the mouth, it picks up other stuff along the way: food debris, bacterial cells, and white blood cells. Humans produce a lot of spit — adults outturn .5 to 1.5 liters of saliva daily, enough over a lifetime, one person’s spit could fill two swimming pools. Glands in the mouth are constantly secreting spit, but the mere thought of food causes a rapid increase.

Douglas Granger, one of the foremost experts on spit, describes saliva as “the diagnostic fluid of the future.” Here are four pretty cool things that spit can do that may surprise you.

Spit Reveals Levels of Stress and Anxiety

Saliva has varying levels of cortisol, also known as the “stress hormone”. When this happens, the reaction isn’t just psychological; higher levels of cortisol in spit are associated with physiological effects like reduced immune function, longer recovery time, increased blood pressure, and increased heart rates. This has been found to be true for both humans and dogs.

Accordingly, salivary cortisol is also an indicator of anxiety levels. In a 2010 study of 170 children, researchers found that children with higher self-reported levels of anxiety also had higher levels of salivary cortisol — potentially acting as an evaluative first step to test for levels of anxiety.

Spit Helps With Disease Diagnosis

Saliva is increasingly being compared to blood as a way to sample the body for disease and other physiologic symptoms. A few things spit can tell medical personnel: whether a person has been exposed to chemical exposures, environmental detriments like smoke, even the potential for heart disease. Researchers at the Johns Hopkins School of Nursing are developing a way to detect the presence of HIV through examination of saliva, while Swedish researchers at Malmö University are currently studying whether cancer leaves its presence in saliva as well. It’s fair to say that a couple drops of saliva might be able to replace blood tests.

Spit isn’t poised to completely replace blood tests, but it may become a less invasive way to reveal inner chemistry; in a 2012 paper, Douglas Granger writes, “As a gateway to the body, the mouth senses and responds to the external world and reflects what is happening inside the body.”

Analyzing Spit Can Aide Athletes

Because spit can be analyzed for what are called biomarkers, sports programs — like the football program at the University of Nebraska-Lincoln — are beginning to analyze the spit of their athletes. Investigation of player’s spit helps sports doctors look out for concussion biomarkers and chart athletes’ circadian rhythms, helping athletes know if they’re overtraining. Saliva can also be used as a tool to monitor steroid, peptide, and immune markers — by examining proteins in spit, doctors can also see if athletes are susceptible to upper respiratory tract infections.

Engineers at the University of California, San Diego have capitalized on this knowledge and have developed a mouth guard that monitors health markers like lactate, cortisol, and uric acid within saliva. A buildup of uric acid is correlated with developing the form of arthritis, gout.

Spit Can Benefit Crime Scene Investigators

In 2011, researchers at the University of California, Los Angeles came across an incredible discovery: spit can reveal someone’s age. The researchers then developed a salivary test that forensic investigators could use to pinpoint a suspect’s age. All it takes is one sample — like a trace of saliva left on a cup — to determine an individual’s exact age. Great news if you’re a cop, terrible news if you’re a bank robber prone to spitting.

Photos via Giphy (1, 2, 3, 4, 5)