Saliva

What is saliva?

Saliva (spit) is a watery liquid your salivary glands release into your mouth. Saliva has several functions, like aiding digestion and protecting your teeth. It’s mostly water but contains many important proteins and other substances, as well.

Healthcare providers can use saliva samples for several tests. They can detect things like cortisol levels and substance use (through drug tests). Tests on saliva samples can also detect viruses like HIV and identify other kinds of infections.

What is the purpose of saliva (spit)?

Saliva plays several important roles in supporting your oral and overall health. Saliva:

• Keeps your mouth and throat moist and comfortable: Saliva protects the mucosae (mucus membranes) of your mouth from sticking to each other with the help of mucous secretions. This provides a lubricating barrier all over your mouth, protecting your mucosa from harmful substances (like bacteria and toxins) and injury.
• Moistens food so it’s easier to chew and swallow: When you eat, the food leaves your mouth and travels down your throat, through your esophagus and eventually makes its way to your stomach. Saliva moistens your food and turns it into a small ball (bolus) that makes its journey down your throat and esophagus smoother. If you had no saliva or moistness in your food, swallowing would be almost impossible.
• Starts the digestion process: Saliva contains an enzyme called amylase, which helps your stomach break down starches in food.
• Protects against infection: Saliva contains lysozyme, an enzyme that disintegrates many bacteria and prevents the overgrowth of oral microbial populations in your mouth.
• Protects your teeth: Saliva contains calcium hydroxyapatite, which prevents calcium loss (demineralization) from your teeth. Saliva cleans your teeth by washing away bits of food debris. It also helps “dilute” acidic foods you chew to protect your teeth from erosion. Overall, it helps reduce your risk of cavities and gum disease.
• Helps maintain the pH balance in your mouth: Saliva helps maintain a pH range of 6.0 to 7.5 within your mouth. Different foods you eat have different pH levels. Saliva helps rebalance your mouth’s pH level after you swallow food.
• Helps repair tissue in your mouth: Saliva has certain proteins and growth factors that work to regenerate tissue and promote wound healing. If you bite the inside of your cheek, for example, your spit can start the healing process.
• Helps you taste food: Dry foods need moisture for your taste buds to pick up on their flavors. Saliva provides this moisture.

Where does saliva come from?

Saliva (spit) comes from your salivary glands. They produce saliva and release it into your mouth through ducts, or small openings.

You have three major pairs of salivary glands:

• Parotid glands: Your parotid glands are just in front of your ears. The saliva produced by your parotid glands enters your mouth from small ducts near your upper molars. These are the largest salivary glands.
• Sublingual glands: These are below either side of your tongue, under the floor of your mouth.
• Submandibular glands: These are below your jaw. Like your sublingual glands, the saliva from your submandibular glands enters your mouth from under your tongue.

These glands contribute to 90% of your total saliva secretions. Minor salivary glands (you have hundreds of them) contribute to the remaining 10%. Salivary glands make about 0.5 to 1.5 liters (2 to 6.3 cups) of saliva a day in most adults.

What triggers salivation?

Your autonomic nervous system (ANS) mainly controls salivation. Your ANS is a part of your overall nervous system that controls the automatic functions of your body that you need to survive. These are processes you don’t think about that your brain manages while you’re awake or asleep.

Two divisions of your ANS are responsible for salivation:

• Sympathetic nervous system: This system activates body processes that help you in times of need, especially times of stress or danger. This system is responsible for your body’s “fight-or-flight” response. Stimulation of your sympathetic nervous system produces more viscous (thick) saliva. This helps explain why you may have a dry mouth during times of stress or anxiety.
• Parasympathetic nervous system: This part of your ANS does the opposite of your sympathetic nervous system. It’s responsible for the “rest-and-digest” body processes. Stimulation of your parasympathetic nervous system produces more watery saliva. Watery saliva helps you chew and swallow food more easily.

Parasympathetic stimulation of your salivary glands has a more significant and longer-lasting effect on salivation than sympathetic stimulation.

Certain everyday situations and foods can affect the level of salivation, for example:

• Your salivary glands generally produce more saliva when you eat sour foods. This is because they have more acid than other foods. Extra saliva dilutes the acid to help protect your teeth and your digestive system from its corroding effects.
• Just thinking about food can make you salivate, especially foods that you think of as particularly delicious.
• Your salivary glands are more active during the day. The flow of saliva decreases considerably at night. Researchers think this is a circadian rhythm-related process.

What is saliva made of?

Saliva is 99% water and 1% proteins, electrolytes and other substances. 

Researchers have identified over 1,000 proteins in saliva. But only around 10% of them are in high abundance. Proteins are large, complex molecules that do most of the work in cells (not to be confused with the macronutrient protein). They have several important roles. Examples of some of the most prevalent proteins in your saliva include:

• Amylase: Amylase is an enzyme (special protein) that helps you digest carbohydrates. Your pancreas and salivary glands mainly make amylase. Most of your body’s amylase is in your spit, but there can be some in your blood and pee, as well.
• Proline-rich peptides (PRPs): PRPs are a large family of salivary proteins that your parotid and submandibular glands produce. They make up nearly 70% of the total protein of your saliva. Acidic PRPs, for example, bind to a substance and form a film on your teeth called a pellicle. This helps protect your teeth.
• Host-defense peptides: These peptides are part of your body’s immune system. They have important roles in your body’s response to infection and inflammation.
• Mucins: These large proteins play a significant role in lubricating the structures in your mouth (like your tongue and gums). They form a physical barrier to help block harmful bacteria, fungi and viruses.
• Secretory IgA: This is an antibody that binds to pathogens (harmful substances) and commensal microbes (microbes in your mouth that don’t cause harm). Secretory IgA is a part of your body’s defense system and keeps you and your mouth healthy.

Saliva contains other organic components, like:

• Glucose (sugar).
• Urea (a waste product).
• Cortisol (the “stress hormone”).
• Sex hormones (like estrogen and testosterone).
• Substances that are specific to your blood type.

What are the common conditions related to saliva?

Several conditions and medical treatments (like medications and radiation therapy) can affect the amount and quality of your saliva.

The two main problems related to saliva are hyposalivation (lack of saliva) and hypersalivation (too much saliva). Hyposalivation is more common. Both conditions can be temporary or chronic (long-term).

Hyposalivation

Hyposalivation means your salivary glands don’t produce enough saliva. It’s also called salivary gland hypofunction. This leads to dry mouth (xerostomia).

A lack of saliva can cause problems, including:

• Bad breath (halitosis).
• Mouth and throat discomfort.
• Oral hygiene problems, including cavities, tooth decay and other mouth diseases.
• Problems wearing dentures.
• Trouble with speech and swallowing.

Some medical conditions that can cause a lack of saliva include:

• Dehydration.
• Certain autoimmune conditions, including Sjögren’s syndrome, lupus and rheumatoid arthritis.
• Viral infections, like HIV and hepatitis C.
• Poorly managed diabetes, which leads to consistently high blood sugar levels and dehydration. 
• Alzheimer’s disease.
• High blood pressure (hypertension).

A dry mouth is a side effect of more than 500 medications. Common medications that can cause dry mouth include:

• Antianxiety medications and antidepressants.
• Anticholinergics. These medications treat many conditions, like urinary incontinence, overactive bladder and chronic obstructive pulmonary disease (COPD).
• Antihistamines, decongestants and some pain medicines.
• Certain blood pressure medications, like beta-blockers.
• Chemotherapy medications.
• Parkinson’s disease medications.

Radiation therapy, especially for head and neck cancer, is also a common cause of hyposalivation.

Hypersalivation

Hypersalivation (sialorrhea) happens when your salivary glands make too much saliva. This can lead to drooling. Excess saliva isn’t the only cause of drooling — weakness in certain muscles in your mouth or throat can cause it, too. This is why babies drool.

Severe or chronic drooling can lead to health problems. For example, excessive drooling can cause angular cheilitis — a skin condition that involves painful, cracked sores at the corners of your mouth. In extreme cases, excess saliva can lead to aspiration or choking. This can cause aspiration pneumonia.

Hypersalivation can be a side effect of certain medications, especially antipsychotic medication. Clozapine is an example of one of these medications.

Certain conditions can cause excess saliva as well, including:

• Untreated cavities: Cavities cause bacteria on your teeth and in your mouth. This may prompt your salivary glands to produce more saliva to try to keep your mouth clean.
• Gastroesophageal reflux (GERD): GERD causes stomach acid to flow into your esophagus. This triggers your salivary glands to release saliva in an effort to keep the stomach acid out of your mouth.
• Nausea: If you’re on the verge of vomiting, your salivary glands usually release extra saliva to keep stomach acid in the vomit from damaging the inside of your mouth.
• Pregnancy: Excess saliva can be a temporary side effect of pregnancy. Your salivary glands become overstimulated. Nausea during pregnancy can also contribute to excess saliva.

When should I see my doctor about saliva problems?

If you have a dry mouth or excess saliva that’s not going away, see your healthcare provider. They can do a physical exam and order some tests to find the underlying cause. Certain treatments can help.

Why is my saliva so thick?

Thick or sticky saliva happens when there’s less water in it than usual. Sometimes, mucus mixes with your saliva and contributes to this “thick” or “sticky” feeling.

Several things can cause it, like dehydration, smoking and chronic allergies. The main way to fix thick spit is to stay hydrated by drinking more water. If you have long-term thick saliva, talk to your healthcare provider. There may be something else at play.

A note from Cleveland Clinic

Saliva is typically something we don’t think about until we have too much or not enough of it. It’s an important and busy fluid that’s essential to your well-being. If you have concerns about your saliva or your oral health in general, it’s important to talk about it with your healthcare provider. They can help you figure out the problem and recommend treatments.