You probably don’t think about saliva all that much. You know it’s there, and you might know that it helps kick off the digestive process. But is that it? Spoiler alert: It’s not.
Saliva is a complex fluid with a wide range of jobs. We’ll cover just some of these jobs today.
Although it might seem like an unsavory subject, we’re confident you’ll view drool in a new light after reading this.
So, let’s leap headlong into a vat of saliva science.
1. Saliva contains more than 1,000 compounds
Mostly, saliva is water — about 99.5%. The rest is a complicated mix of proteins, salts, and other compounds.
Scientists have identified more than 1,000 different proteins in saliva. And they carry out a dizzying array of jobs.
Among them are immune system components, enzymes, bacteria-fighting proteins, and factors that support growth and repair.
And aside from proteins, saliva also contains:
electrolytes, including potassium, magnesium, calcium, and phosphate
mucus, which contains water, proteins, salts, and sugars
short chains of amino acids, like opiorphin, a painkiller
bacteria — around 1 billion bacteria per milliliter, though the numbers vary greatly throughout the day
human cells — about 500,000 per ml of saliva
2. You have more than 1,000 salivary glands
Saliva is created in your aptly named salivary glands. About 90% of it is produced by the three "major" salivary glands:
parotid: just in front of your ears
submandibular: beneath your lower jaw
sublingual: below your tongue
An incredible 1,000 minor salivary glands produce the remaining 10% of your saliva.
And it comes in different forms: Serous saliva is watery, mucous saliva is thicker, and mixed saliva is somewhere in between.
3. You produce up to 2.5 pints of saliva each day
When the secretion of saliva is stimulated, for instance, when you’re chewing food, you produce up to 7 ml per minute.
Even when your mouth is unstimulated, you produce around 0.3–0.4 ml per minute. However, this figure varies a great deal between individuals.
In total, each day, you produce an impressive 0.9 to 2.5 pints (0.5 to 1.5 liters) of saliva.
Interestingly, a range of surprising factors can influence how much saliva you produce when you’re unstimulated. These include:
Body position: When you’re standing, you produce more saliva than when you’re sitting.
Daily rhythms: You produce the most saliva during the afternoon and hardly any during sleep.
Seasonal changes: There’s some evidence that you produce the most saliva in winter and the least in summer. This may be due to dehydration in the hotter months.
4. Sour flavors stimulate the most saliva
A small study of eight participants investigated which flavor triggers the greatest release of saliva.
It found that a sour flavor stimulated the most. This is how the flavors ranked from highest to lowest:
sour: citric acid
savory or umami: monosodium glutamate, better known as MSG
bitter: magnesium sulfate
5. Saliva protects your mouth
Saliva helps protect the inside of your mouth as you eat, chew, and talk. People with xerostomia — a condition in which you don’t produce enough saliva — often have sore mouths.
These folks also find that without the lubrication of saliva, dry foods, in particular, stick to the insides of their mouths. And they can find swallowing difficult for the same reason.
In people with healthy levels, saliva helps soften and lubricate hard foods, making them less likely to scratch the inside of your mouth and throat.
Saliva may also offer some protection against burns from hot foods and drinks, simply by diluting the contents of your mouth.
And saliva can protect against acid, too.
You may have noticed that your mouth fills with saliva just before you vomit. Because your stomach contents are notoriously acidic, this influx of saliva might help protect your teeth and the inside of your mouth.
6. Saliva starts the digestive process
Saliva gets the work of digestion started as soon as food enters your mouth. Among its various enzymes is amylase, which breaks down starch into simpler sugars.
Weirdly, you produce more amylase when you’re stressed, for instance, before a skydive.
Saliva also contains salivary lipase, which starts the breakdown of fats. However, according to experts, salivary lipase doesn’t play a particularly important part in digestion.
It seems more important for flavor perception, as we’ll discover next.
7. Without saliva, food wouldn’t be as tasty
People with xerostomia, a lack of saliva, often experience distorted taste, which is called dysgeusia. For instance, they sometimes report that things taste metallic.
It turns out that saliva plays a big part in how you perceive flavor. First, because it’s fluid, it helps ferry chemicals from food to your taste receptors.
Also, saliva helps release odors from the food in your mouth. And because smell is an important part of taste, this enhances the flavor.
Saliva’s enzymes play a role, too. As amylase breaks starch into simple sugars, it allows you to taste the sweetness of starchy foods. Without amylase, many foods that contain carbs might taste quite different.
Similarly, salivary lipase breaks down fat and helps unlock its flavor. Scientists have shown that if they block lipase activity, study participants find it harder to tell whether they're eating fats.
Researchers are still investigating the role of saliva in taste, but it seems that a range of proteins in saliva might play a part, including leptin, ghrelin, and insulin.
Join our mailing list
Sign up for fresh insights into our scientific discoveries and the latest nutrition updates. No spam, just science.
We might be tempted to overlook the importance — why would saliva make such an effort just to ensure you can enjoy the complex flavors of your morning coffee?
But in the wild, where food safety laws don’t exist, flavor can be a matter of life and death: Before you swallow, it’s vital to discern whether something will provide you with life-giving nutrients or life-threatening food poisoning.
8. Saliva protects you from invading microbes
Because your mouth is warm, damp, and open to the outside world, it faces an almost constant battle with microbial invaders. Your saliva, however, has your back.
Some authors have called saliva the “gatekeeper of the oral cavity.” And it approaches its microbial foes with a multipronged attack.
For instance, saliva contains proteins called agglutinins that clump bacteria together, making them easier to clear as you swallow. And proteins called mucins stop bacteria from sticking to surfaces like your teeth.
Another protein — lactoferrin — binds to iron. This means that bacteria, which need iron to survive, can’t access it and die.
Some other enzymes in saliva lead to the production of compounds that are toxic to bacteria. And others can puncture microbes’ cell walls, killing them by emptying their contents.
Although we’ve not covered it all, that’s already an impressive array of defenses.
But what’s perhaps even more impressive is that, while it's killing some microbes, saliva can also help support “good” bacteria.
Like your gut, your mouth hosts bacteria that benefit health. Although we know very little about how the oral microbiome functions, scientists think that compounds in saliva help feed “good” microbes.
9. Saliva helps you heal wounds
An animal with a mouth wound that keeps it from eating might not survive very long.
So, if injuries do happen, your body must heal them quickly. And saliva has, once again, got your back.
Saliva likely helps you heal faster in several ways.
For instance, there’s evidence from animal studies that a compound called salivary vascular endothelial growth factor plays a part by rebuilding the lining of your mouth and supporting the growth of new blood vessels.
And laboratory research suggests that other compounds, called histatins, might also help close wounds and rebuild the lining of your mouth.
Because scientists have noted that wounds in the mouth heal quickly and often without scarring, some are investigating ways to use human saliva to help wounds on your skin heal quicker.
Thanks for joining us on this journey; you’re now within spitting distance of the finish line.
We hope you’ll leave this article with a newfound appreciation for saliva. Without it, life would be much less flavorful — and perhaps shorter.
Saliva enhances our enjoyment of food, protects against microbes and poisons, helps you swallow, looks after your teeth, and heals wounds. You certainly wouldn’t want to be without it.
A review of saliva: Normal composition, flow, and function. The Journal of Prosthetic Dentistry. (2001). https://www.sciencedirect.com/science/article/pii/S0022391301540329
Dysgeusia. (2021). https://my.clevelandclinic.org/health/diseases/22047-dysgeusia
Food-saliva interactions: Mechanisms and implications. Trends in Food Science & Technology. (2017). https://www.sciencedirect.com/science/article/pii/S0924224417300092
Histatins are the major wound-closure stimulating factors in human saliva as identified in a cell culture assay. The FASEB Journal. (2008). https://faseb.onlinelibrary.wiley.com/doi/abs/10.1096/fj.08-112003
Hormonal responses to psychological stress in men preparing for skydiving. The Journal of Clinical Endocrinology & Metabolism. (1997). https://academic.oup.com/jcem/article/82/8/2503/2877639
Human saliva stimulates skin and oral wound healing in vitro. Tissue Engineering and Regenerative Medicine. (2019). https://onlinelibrary.wiley.com/doi/full/10.1002/term.2865
Molecular mechanisms of taste recognition: Considerations about the role of saliva. Molecular Sciences. (2015). https://www.mdpi.com/1422-0067/16/3/5945
Quantifying live microbial load in human saliva samples over time reveals stable composition and dynamic load. mSystems. (2021). https://journals.asm.org/doi/full/10.1128/mSystems.01182-20
Revised estimates for the number of human and bacteria cells in the body. PLOS Biology. (2016). https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002533
Role of salivary vascular endothelial growth factor (VEGF) in palatal mucosal wound healing. Wound Repair and Regeneration. (2013). https://onlinelibrary.wiley.com/doi/10.1111/wrr.12065
Saliva: An all-rounder of our body. European Journal of Pharmaceutics and Biopharmaceutics. (2019). https://www.sciencedirect.com/science/article/pii/S0939641119303704
Saliva and oral health 4th edition. (2012). https://stage.wrigleyoralcare.com/s3media/2022-02/SHL_S_OH_A5_2015_FINAL.pdf
Saliva between normal and pathological. Important factors in determining systemic and oral health. Journal of Medicine and Life. (2009). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5052503/
Salivary amylase – the enzyme of unspecialized euryphagous animals. Archives of Oral Biology. (2015). https://www.sciencedirect.com/science/article/pii/S0003996915001259
Salivary factors that maintain the normal oral commensal microflora. Journal of Dental Research. (2020). https://pubmed.ncbi.nlm.nih.gov/32283990/
Salivary lipase and alpha-amylase activities are higher in overweight than in normal weight subjects: Influences on dietary behavior. Food Research International. (2014). https://www.sciencedirect.com/science/article/pii/S0963996914006541
Salivary opiorphin in dental pain: A potential biomarker for dental disease. Archives of Oral Biology. (2019). https://www.sciencedirect.com/science/article/pii/S0003996918304709
The effect of monosodium glutamate on parotid salivary flow in comparison to the response to representatives of the other four basic tastes. Physiology & Behavior. (2006). https://www.sciencedirect.com/science/article/pii/S0031938406003623
The fatty acid translocase gene CD36 and lingual lipase influence oral sensitivity to fat in obese subjects. Journal of Lipid Research. (2012). https://www.sciencedirect.com/science/article/pii/S0022227520413720
The functions of human saliva: A review sponsored by the World Workshop on Oral Medicine VI. Archives of Oral Biology. (2015). https://www.sciencedirect.com/science/article/pii/S0003996915000692
The power of saliva: Antimicrobial and beyond. PLOS Pathogens. (2019). https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1008058
The proteomes of human parotid and submandibular/sublingual gland salivas collected as the ductal secretions. Journal of Proteome Research. (2008). https://pubs.acs.org/doi/10.1021/pr700764j
Xerostomia. (2022). https://www.ncbi.nlm.nih.gov/books/NBK545287/