Salivary gland stones form when minerals in your saliva, primarily calcium and phosphate, crystallize and harden inside a salivary duct or gland. The process typically begins with a slowdown in saliva flow, which allows mineral-rich saliva to pool and gradually solidite into a stone. These stones, called sialoliths, affect roughly 2 out of every 100,000 people and are most common in adults over 40.
How Stones Form Step by Step
The formation process starts with stagnation. When saliva doesn’t flow freely through the ducts, it sits in place long enough for dissolved minerals to begin clumping together. A small core of organic material, made up of cellular debris, proteins, and sugars naturally present in saliva, acts as a seed. Calcium and phosphate ions in the stagnant saliva deposit onto this core in layers, much like sediment building up in a pipe.
Over time, bacteria from the mouth can travel backward into the duct system. This retrograde contamination adds to the organic debris and creates an environment that accelerates mineral buildup. The stone grows slowly, sometimes over months or years, until it’s large enough to partially or fully block the duct.
Several things can reduce saliva flow and set this process in motion. Narrowing (strictures) of the duct, external pressure from a nearby growth, mucus plugging, and even congenital duct abnormalities can all slow saliva down enough for minerals to precipitate. Radiation therapy to the head or neck and certain immune-related conditions that damage the glands can also reduce output.
What the Stones Are Made Of
Salivary stones are a mix of organic and inorganic material. A study analyzing stone composition found carbonate apatite, a calcium-based mineral, in 99% of stones examined. Phosphate was present in 88%, calcium in 87%, and magnesium in 68%. Less common components included struvite (44%), oxalate (38%), and carbonate (35%). The organic portion consists of proteins, sugars, and dead cell fragments that form the scaffold the minerals build on.
This composition explains why the submandibular gland, located beneath the jaw, produces the vast majority of salivary stones. The saliva it makes is thicker and more alkaline than saliva from other glands, and it contains higher concentrations of calcium and phosphate. The duct also runs upward against gravity, which naturally slows drainage and gives minerals more time to settle out.
Dehydration and Lifestyle Factors
Dehydration is one of the most commonly cited risk factors. When you’re not drinking enough water, your body produces less saliva and what it does produce is more concentrated with minerals. That combination of reduced flow and higher mineral content creates ideal conditions for stone formation. Cleveland Clinic lists dehydration alongside smoking as a contributing factor.
The role of smoking and alcohol is less clear-cut than you might expect. A case-control study published in the Journal of Cranio-Maxillofacial Surgery found no statistically significant correlation between salivary stone formation, smoking, or alcohol consumption. The same study concluded that systemic diseases, medications, smoking, and alcohol play “no or only a limited role” in stone onset. This doesn’t mean these factors are irrelevant to salivary health broadly, but the direct link to stone formation specifically appears weaker than once assumed.
Do Medications Increase Your Risk?
Medications that dry out your mouth are a logical suspect. Hundreds of common drugs reduce saliva production as a side effect, including antihistamines, blood pressure medications, antidepressants, and drugs used for overactive bladder. The mechanism makes theoretical sense: less saliva means more stagnation, which means more opportunity for minerals to crystallize.
However, the research connecting medication use directly to stone formation is surprisingly thin. The same case-control study that examined systemic diseases found that medication use did not show a significant association with salivary stones. This may mean that drug-induced dry mouth alone isn’t enough to trigger stone formation without other contributing factors, or it may reflect how difficult it is to study a condition that develops slowly over months or years.
Age and Other Risk Patterns
Age is one of the strongest predictors. Data from a Taiwanese nationwide health database spanning nearly two decades found that adults over 65 had more than double the risk of salivary stones compared to those under 40. The average age at diagnosis also rose over the study period, from about 38 years old in 1996 to 46 years old by 2013.
This age trend makes biological sense. Saliva production gradually declines as you get older, and the composition of saliva shifts toward higher mineral concentrations. Older adults are also more likely to take medications that reduce saliva flow and to have chronic conditions affecting the glands. These factors compound over time, giving minerals more opportunities to accumulate.
Why the Submandibular Gland Is Most Affected
About 80 to 90% of salivary stones occur in the submandibular gland, and the anatomy explains why. The submandibular duct (Wharton’s duct) is longer than the ducts of other salivary glands, and it takes a sharp upward turn from the gland to its opening under the tongue. Saliva has to flow against gravity to exit, which naturally slows its movement. The saliva itself is thicker, more mucus-rich, and carries more calcium than the watery saliva produced by the parotid gland near the ear.
Parotid stones do occur but are far less common. When they form, the primary driver is typically a structural problem, such as a duct stricture, external compression, or a congenital abnormality, that physically blocks flow rather than the chemical composition of the saliva itself.
Conditions That Were Ruled Out
It’s worth noting what doesn’t appear to cause salivary stones. Despite reasonable assumptions, research has not established a clear link between salivary stones and conditions like gout, kidney stones, or high blood calcium levels. While all of these involve excess minerals in the body, the chemistry of salivary stone formation appears to be driven more by local factors inside the duct, such as flow rate and saliva composition, than by systemic mineral imbalances. The case-control study examining these connections found that systemic diseases played little to no role in stone development.