Often overlooked in our understanding of health, saliva performs several critical functions in the human body.
Although saliva largely consists of water, it also contains electrolytes, mucus, and enzymes. Combined, these elements give saliva several properties that prevent cavities, carry chemicals to taste buds, allow for DNA testing, and facilitate digestion.
“Saliva, as far as dental health, is huge,” Dr. Jonathan Frankel of Frankel Dentistry in Toledo said. “It contains enzymes like amylase. Those enzymes actually break down food and they help you with digestion. It helps wash away bacteria and helps neutralize your saliva so you can digest your food.”
Over the course of a day, the average human will generate between 0.5 to 1.5 liters of saliva. When the body does not produce sufficient saliva, however, significant problems can arise.
First, without saliva, there would be no liquid to send the chemicals from food to taste buds across the mouth, leaving those with dry mouth complaining about decreased sense of taste. Second, dry mouth can make it extremely painful and difficult to chew and swallow. And third, it can also cause tooth decay.
Sleep apnea can cause dry mouth, as breathing through the mouth will dry it out. So can drinking too much pop, as it alters the acidity of saliva. However, the primary concern for dentists today is that many prescription medicines, including Benadryl, Adderall, antihistamines, antidepressants, and opioids, can all lead to dry mouth.
“There’s a multitude of medications that can dry out your mouth, and that’s all lack of saliva,” Dr. Frankel said. “We see people, they have rampant decay, those patients that have dry mouths. You see that a lot more in older patients.”
Salivary glands
There are three primary pairs of salivary glands – the parotid, submandibular, and sublingual – that produce 90 percent of saliva in the human mouth, with 1,000 minor glands responsible for the remaining 10 percent.
While external factors like medication or sleep apnea can cause dry mouth, it is relatively rare to see diseases or malfunctions of the salivary glands themselves.
The more prominent issue stems from tumors that can grow on the glands. These tumors do not have a significant effect on saliva production. However, they can occasionally be cancerous.
Dr. Andrew Rosko, who treats tumors and cancers in the head and neck at ProMedica, explained that salivary gland tumors are most commonly found in the largest gland, the parotid, but 80 percent of those are benign. However, tumors on the smaller glands are more likely to be cancerous.
He explained that after identifying the tumor, the first step is usually a relatively straightforward removal procedure.
“Most of them are random,” Dr. Rosko said. “There’s one kind of tumor called Warthin’s that’s a completely benign tumor, doesn’t need to be removed unless it’s causing problems, but that’s caused by smoking. But that’s benign. The cancers are random.”
In terms of identification, tumors can sometimes manifest themselves as masses in the neck area. In other cases, patients will report discomfort. And perhaps the most common way that doctors uncover tumors is through a CT scan or MRI for other reasons, and they show a tumor.
Saliva in DNA testing
Outside the realm of health, saliva serves as a valuable tool for DNA identification.
Hallie Dreyer, a DNA laboratory supervisor for the Ohio Attorney General’s Office, explained that body fluids like saliva can play a particularly important role in criminal investigations.
“Overall, body fluids such as saliva, blood, or semen are very good sources of DNA,” Ms. Dreyer said. “So we can use that when we need to obtain and generate a DNA profile for comparison purposes.”
Specifically, different people shed skin cells at very different rates, making those less reliable as samples. In comparison, liquid body fluids are generally much easier to work with.
Since blood is most obviously identifiable at a crime scene, that will generally serve as the sample collected from a crime scene. However, saliva is generally the easiest to test as a comparison, with a simple swab of the mouth typically providing sufficient DNA for the state to test.
For ancestry testing companies, they typically require closer to a full vial of saliva to ensure they have enough DNA for all of the panels they run, Ms. Dreyer explained.
Saliva in other animals
Most other mammals produce saliva similarly to humans. It still functions as a digestive and moisturizing agent in the mouth. However, symptoms of sickness present very differently.
Dr. Genevieve Dumonceaux, the director of animal health and nutrition at the Toledo Zoo, explained that diseases in other mammals, especially viruses like rabies, typically present with excess saliva. When cats experience nausea, one symptom is producing too much saliva and swallowing it back down.
Kent Bekker, the zoo’s chief mission officer & senior vice president, elaborated on another significant difference between some animals and humans in terms of saliva.
“Venom is nothing more than modified saliva to begin with,” Mr. Bekker said. “It’s just a saliva with crazy enzyme properties. … Venom is basically doing the work of digestion before the animal even recovers the prey, so, at a fundamental level, while it’s much more dangerous, it’s kind of doing the same thing, so you can see how it’s evolved from salivary glands.”
Whether in animal venom, DNA testing, or simple dental hygiene, it is clear that saliva is nothing to spit at.
Contact Andrew Cramer at acramer@theblade.com
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