SCIENCE

Spit it out: the science of saliva

Betty Zou, Ph D.

When was the last time you heard someone gushing about saliva? Probably never, right? Most drool dialogue you hear is related to either babies and teething or dogs and llamas but not the essential role that spit plays in oral health.

Before we dive into the significance of saliva, let’s take a step back for a quick primer on what spit is. Saliva is a fluid that’s produced by the salivary glands and secreted into the mouth. It is 99% water with the remaining 1% made up of proteins and electrolytes like sodium, potassium and calcium.

On average, the amount of saliva that flows through the mouth of a healthy adult each day is estimated to be between 1 and 1.5 liters. So just what is all that spit doing?

For starters it clears away food, bacteria and debris from the mouth. Saliva also protects the mouth from injuries by softening and lubricating the foods we eat. Without a coating of spit, foods like potato chips and crusty breads would scratch the inside of our mouths with their hard surfaces.

One of saliva’s roles is to maintain the hard surfaces of teeth. It does this by buffering against acid and forming a protective shield over tooth enamel. Under resting or non-eating conditions, saliva flows at a slow rate and contains very low levels of bicarbonate, a chemical that can neutralize acids. When saliva flow is stimulated by taste and chewing, however, bicarbonate levels increase to counteract the acidity brought on by the consumption and breakdown of food. Spit is also a key player in the formation of dental pellicle, a layer of protein on top of tooth enamel. The pellicle starts to form within seconds of clean enamel being exposed to saliva. The proteins, most of which come from saliva, serve as a lubricant to reduce friction between teeth and hard objects such as other teeth, food and a toothbrush. In doing so, it helps to protect the underlying tooth enamel from being worn away by abrasion.

Another important function of saliva is to keep the oral microbial community in check. The constant flow of drool down your throat helps remove sugars and other remaining food matter that can be fermented by bacteria into enamel-eroding acid. Saliva flow also sweeps away free-floating microbes thereby helping to control plaque buildup and reduce the chances of infection. Among the proteins found in saliva are a number with antimicrobial properties. These function in myriad ways to prevent harmful microbes from taking hold in the oral cavity and causing disease. Some proteins cause bacteria to clump together so that they are more easily cleared away while others remove nutrients like iron from the environment so that microbes can’t use them to grow. One family of saliva proteins called histatins has been shown to have antifungal properties against the yeast Candida albicans which causes oral thrush.

Saliva plays such a critical role in oral health that people who produce low amounts of saliva—whether due to aging or an underlying medical condition—are at higher risk of tooth decay. With a low flow, fermentable sugars aren’t cleared away and bicarbonate levels aren’t high enough to act as an effective buffer against acid. The result is a drop in pH as the oral environment becomes more acidic and causes damage to tooth enamel.

In the realm of oral health, saliva is the unsung hero. It’s time that it receives the recognition that it deserves. Spit spit hooray!

Betty Zou, Ph D.

Scientist turned science writer and communicator. I turn complex scientific concepts and studies into clear and engaging content for diverse lay audiences. Previous work include blog posts, news articles and releases, patient and customer profiles, feature length stories, donor reports and marketing materials. My areas of expertise are molecular biology, microbiology and microbiome-related topics but I have also written extensively about other health and medicine topics such as cancer, cardiology and trauma.

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