Saliva has gotten a bad rap for more than a century. In the early 1900s, New York City health officers dubbed “The Sanitary Squad” arrested and fined hundreds of people who spit on subway platforms. Similar arrests during the influenza pandemic of 1918-19 likely limited the spread of the flu. In Goodyear, Arizona, it’s illegal to spit on sidewalks. And if you spit in a public space in Singapore, police officers may fine you.
But while saliva is proficient at transmitting germs, it’s a critical component of our dental and digestive health. It plays a vital role in maintaining physical wellbeing, and it’s a key player in the process of eating and digestion. Without enough saliva — as anyone who’s suffered dry mouth can tell you — a multitude of problems can occur.
The How and When of Saliva
As an autonomous bodily function — that is, something we do without having to think about it — saliva doesn’t usually inspire much contemplation unless you’re sidestepping a glob of it on your favorite outdoor exercise route. Still, scientists have long known that spit is powerful stuff. Without it, our mouth would be a cesspool of infection.
Three pairs of major glands and numerous other minor glands surrounding our oral cavity generate saliva. Tubes called salivary ducts carry it to the mouth. Healthy humans produce between two and six cups of saliva a day. Saliva production is a near-constant process, though we tend to produce more in the late afternoon. (That’s enough spit over a year, by the way, to fill an entire bathtub.)
We most often salivate when we’re eating or even just thinking about delicious food (see Pavlov’s famous dog and bell experiment). Salivation is a good thing — as long as we remember to wipe the drool off our chin — because spit includes a wealth of beneficial components.
A Magical Mixture
What’s in this magical liquid, comprised of 99 percent water? Saliva represents a mixture of enzymes and electrolytes, proteins and minerals, antibacterial compounds and mucus. A film of saliva covers our teeth, strengthening them against decay and re-mineralizing tooth enamel with a powerful combination of calcium and other minerals. As it flows around our mouth, it kills germs and flushes away bits of food, which help prevent both gum disease and bad breath.
Saliva also keeps the mouth’s pH levels balanced. What we eat and drink can affect the acidity and alkalinity of our pH. For example, gulping a glass of orange juice adds acidity to your mouth, which can soften the enamel of your teeth. Without saliva to balance out that acidity, you’re at risk of tooth decay and halitosis. (You can test the acidity and alkalinity of your saliva by spitting on a pH strip, available at a local drug store.)
Wound-Healing and Art-Restoration
Saliva is also packed with white blood cells that can help heal wounds. A 2015 study published in the medical journal Blood reported human spit, especially spit collected first thing in the morning, as useful in fighting infection. The liquid is rich in a particular white blood cell called neutrophils, which is adept at killing bacteria. Saliva also promotes blood clotting and contains a painkilling peptide. No wonder dogs and cats lick their sores: They instinctively know the power of spittle.
Thanks to saliva, we can relish the flavor of a succulent slice of mango or a rich molé sauce; it helps to dissolve food chemicals that taste bud receptors can then detect. Saliva also aids in breaking down each delicious mouthful, so we can swallow easily without choking. It protects the esophagus and assists in neutralizing the reflux acids responsible for heartburn.
One particular enzyme, called α-amylase, does more than just help us digest food by breaking starch grains into pieces as we chew. The starch-busting properties of this enzyme are so potent that art restorers have used it since the 18th century. In 2018, Harvard presented its Ig Nobel Prize — awarded annually for unusual and humorous scientific achievements around the world — to a trio of Portuguese scientists who proved the power of human saliva to effectively clean dirt from antique gilded sculptures and paintings.
Too Much Saliva
What happens when you have too much of a good thing? Hypersalivation, or sialorrhea, occurs when our bodies make too much saliva, which may cause us to drool and experience difficulty breathing. Reasons include an inability to close one’s mouth, difficulty swallowing, nasal blockage, dentures or poor alignment of teeth, and oral infections. Even reptile venom and spider bites can cause an excess of saliva. People with sialorrhea may accidentally inhale food and fluids into their lungs, which can lead to aspiration pneumonia.
Doctors may prescribe physical therapy for people who over-salivate. For more severe conditions, they may put a patient on medication, or in extreme cases advise surgery of the salivary glands or ducts.
The Trouble with Dry Mouth
What if — because of health conditions or medications — you’re unable to make enough saliva? In ancient India, a dry mouth could get you in trouble with the law. Authorities believed that anxiety brought on by deceit slowed the flow of saliva. Suspected criminals accused of lying had to chew grains of dry rice. As long as they could spit out grains, they were presumed innocent. But if rice stuck inside the mouth, it indicated a lack of saliva along with certain guilt.
These days, scientists know that dry mouth, or xerostomia, has a wide variety of causes. Diabetes, cancer treatments, and medications all contribute to the condition. People who snore, those who suffer from sinus issues, and people who smoke are at risk for dry mouth. Athletes are prone to xerostomia if they breathe through their mouths during physical activity. Denture-wearers also report issues.
Lack of saliva can cause uncomfortable conditions that range from bad breath and gingivitis to difficulty swallowing and digesting food. People may experience a rough, aching tongue, tooth decay, and an altered sense of taste.
It’s a significant problem, especially as we grow older. More than a quarter (27 percent) of women and 21 percent of men experience xerostomia, and it affects more than 39 percent of adults over age 65. Denture wearers with xerostomia may develop oral thrush, which can spread infection to other parts of the body.
Fortunately, you can take specific actions to mitigate the problems caused by dry mouth.
An Indicator of Health or Disease
Scientists have found that analyzing a saliva sample, instead of the usual blood or urine specimens, can help identify or predict the onset of diseases years before they show up in our bodily tissues. With that in mind, doctors may be able to study our spit and develop personalized measures of protection to lengthen our lifespan.
All this to say that saliva deserves our respect. This constant element of our humanity, while often maligned, protects us from dental disease and keeps us from choking on food. It enhances our taste, helps to heal our wounds, and brightens the artwork in our museums.
Knowing the power in this all-but-invisible substance, it’s no wonder we want to guard the health of our saliva but keep it to ourselves. After all, approximately 80 million bacteria may transfer from one person to another in a 10-second kiss.
However, if you don’t make enough saliva, you have the power to increase it. Take care of your saliva, and it will take care of you.