Infections involving the salivary glands can be viral or bacterial (or rarely fungal).

- Mumps is the most common viral sialadenitis. It usually occurs in children, and there is preauricular pain (pain felt in front of the ear), swelling of the parotid, fever, chills, and headaches.

- Bacterial sialadentitis is usually caused by ascending organisms from the oral cavity. Risk factors include reduced salivary flow rate.

- Human immunodeficiency virus-associated salivary gland disease (HIV-SGD).

A salivary diverticulum (plural "diverticuli") is a small pouch or out-pocketing of the duct system of a major salivary gland. Such diverticuli typically cause pooling of saliva and recurrent sialadenitis, especially parotitis. A diverticulum may also cause a sialolith to form.

The condition can be diagnosed by sialography. Affected individuals may "milk" the salivary gland to encourage flow of saliva through the duct.

The prevalence of salivary stones in the general population is about 1.2% according to post mortem studies, but the prevalence of salivary stones which cause symptoms is about 0.45% in the general population. Sialolithiasis accounts for about 50% of all disease occurring in major salivary glands, and for about 66% of all obstructive salivary gland diseases. Salivary gland stones are twice as common in males as in females. The most common age range in which they occur is between 30 and 60, and they are uncommon in children.

Salivary gland aplasia (also termed salivary gland agenesis) is the congenital absence of salivary glands. Usually the term relates to the absence of some or all of the major salivary glands.

It is a rare condition, and most known cases have been in association with syndromes of the ectodermal tissues, particularly the lacrimal apparatus. Example syndromes which have been reported with salivary gland aplasia include hereditary ectodermal dysplasia, mandibulofacial dysostosis and hemifacial microsomia.

The main significance of the condition is a lack of saliva, causing xerostomia (dry mouth), with accompanying susceptibility to dental caries (tooth decay), infections of the mouth, and upper respiratory tract infections (e.g., candidiasis, ascending sialadenitis, laryngitis and pharyngitis). Patients with salivary gland aplasia typically require regular application of topical fluoride to prevent tooth decay.

In one report, about 20% of individuals with mealtime syndrome had strictures upon sialography. For unknown reasons, strictures seem to be more common in females.

Ectopic salivary gland tissue which is located in sites other than the normal location is variously described as aberrant, accessory, ectopic, heterotopic or salivary gland choristoma.

There are thought to be a series of stages that lead to the formation of a calculus ("lithogenesis"). Initially, factors such as abnormalities in calcium metabolism, dehydration, reduced salivary flow rate, altered acidity (pH) of saliva caused by oropharyngeal infections, and altered solubility of crystalloids, leading to precipitation of mineral salts, are involved. Other sources state that no systemic abnormality of calcium or phosphate metabolism is responsible.

The next stage involves the formation of a which is successively layered with organic and inorganic material, eventually forming a calcified mass. In about 15-20% of cases the sialolith will not be sufficiently calcified to appear radiopaque on a radiograph, and therefore be difficult to detect.

Other sources suggest a retrograde theory of lithogenesis, where food debris, bacteria or foreign bodies from the mouth enter the ducts of a salivary gland and are trapped by abnormalities in the sphincter mechanism of the duct opening (the papilla), which are reported in 90% of cases. Fragments of bacteria from salivary calculi were reported to be Streptococci species which are part of the normal oral microbiota and are present in dental plaque.

Stone formation occurs most commonly in the submandibular gland for several reasons. The concentration of calcium in saliva produced by the submandibular gland is twice that of the saliva produced by the parotid gland. The submandibular gland saliva is also relatively alkaline and mucous. The submandibular duct (Wharton's duct) is long, meaning that saliva secretions must travel further before being discharged into the mouth. The duct possesses two bends, the first at the posterior border of the mylohyoid muscle and the second near the duct orifice. The flow of saliva from the submandibular gland is often against gravity due to variations in the location of the duct orifice. The orifice itself is smaller than that of the parotid. These factors all promote slowing and stasis of saliva in the submandibular duct, making the formation of an obstruction with subsequent calcification more likely.

Salivary calculi sometimes are associated with other salivary diseases, e.g. sialoliths occur in two thirds of cases of chronic sialadenitis, although obstructive sialadenitis is often a consequence of sialolithiasis. Gout may also cause salivary stones, although in this case they are composed of uric acid crystals rather than the normal composition of salivary stones.

The condition is rare. It is more likely to occur in persons who regularly have raised pressure in the mouth, for example wind instrument players, and balloon and glass-blowers. Cases have also been reported with bicycle tyre inflation, whistling, nose blowing, cough and valsalva manoeuvre to clear the ears. It can be an iatrogenic effect of dental treatment, spirometry, and positive pressure ventilation. Apart from these factors, the condition mainly occurs in adolescents, often self-inflicted due to psychological issues.

"Dehydration:"

This is a common, non-infectious cause of parotitis. It may occur in elderly or after surgery.

"Acute bacterial parotitis:"

is most often caused by a bacterial infection of Staphylococcus aureus but may be caused by any commensal bacteria.

"Parotitis as Extrapulmonary Tuberculosis:"

The mycobacterium that cause tuberculosis can also cause parotid infection. Those infected tend to have enlarged, nontender, but moderately painful glands. The diagnosis is made by typical chest radiograph findings, cultures, or histologic diagnosis after the gland has been removed. When diagnosed and treated with antitubercular medications, the gland may return to normal in 1–3 months.

"Acute viral parotitis (mumps):"

The most common viral cause of parotitis is mumps. Routine vaccinations have dropped the incidence of mumps to a very low level. Mumps resolves on its own in about ten days.

"HIV parotitis:" Generalized lymphadenopathy has long been associated with HIV, but the localized enlargement of the parotid gland is less well known.

A salivary gland fistula (plural "fistulae") is a fistula (i.e. an abnormal, epithelial-lined tract) involving a salivary gland or duct.

Salivary gland fistulae are almost always related to the parotid gland or duct, although the submandibular gland is rarely the origin.

The fistula can communicate with the mouth (usually causing no symptoms), the paranasal sinuses (giving rhinorrhea) or the facial skin (causing saliva to drain onto the skin).

The usual cause is trauma, however salivary fistula can occur as a complication of surgery, or if the duct becomes obstructed with a calculus.

Most parotid fistulae heal by themselves within a few weeks.

The lesion is usually present in children. Ranulas are the most common pathologic lesion associated with the sublingual glands.

An "accessory salivary gland" is ectopic salivary gland tissue with a salivary gland duct system. The most common location of accessory salivary gland tissue is an extra major salivary gland in front of the parotid gland. It is typically about 3 cm or less in size, and drains into the parotid duct via a single tributary. Accessory parotid tissue is found in 21-56% of adults. Any disease process which affects the salivary glands, including cancer, may also occur within an accessory salivary gland tissue.

Strictures tend to be diagnosed based on difficulty with insertion and manipulation during sialendoscopy, or by sialography or ultrasound.

Xerostomia is a very common symptom. A conservative estimate of prevalence is about 20% in the general population, with increased prevalences in females (up to 30%) and the elderly (up to 50%).

Xerostomia may be caused by autoimmune damage to the salivary glands. Sjögren's syndrome is one such disease, and it causes other symptoms, including xerophthalmia (dry eyes), dry vagina, fatigue, myalgia (muscle pain), and arthralgia (joint pain). Females are more likely to suffer from autoimmune disease, and 90% of people with Sjögren's syndrome are women. Primary Sjögren's syndrome is the combination of dry eyes and xerostomia. Secondary Sjögren's syndrome is identical to primary form but with the addition of a combination of other connective tissue disorders such as systemic lupus erythematosus or rheumatoid arthritis.

Recurrent pneumoparotitis may predispose to sialectasis, recurrent parotitis, and subcutaneous emphysema of the face and neck, and mediastinum, and potentially pneumothorax.

Minor trauma to the floor of the mouth is thought to damage the delicate ducts that drain saliva from the sublingual gland into the oral cavity. The lesion is a mucous extravasation cyst (mucocele) of the floor of mouth, although a ranula is often larger than other mucoceles (mainly because the overlying mucosa is thicker). They can grow so large that they fill the mouth. The most usual source of the mucin spillage is the sublingual salivary gland, but ranulas may also arise from the submandibular duct or the minor salivary glands in the floor of the mouth. A cervical ranula occurs when the spilled mucin dissects its way through the mylohyoid muscle, which separates the sublingual space from the submandibular space, and creates a swelling in the neck. It may occur following rupture of a simple ranula. Rarely, ranulas may extend backwards into the parapharyngeal space.

Causes of decreased clearance of saliva include:

- Infections such as tonsillitis, retropharyngeal and peritonsillar abscesses, epiglottitis and mumps.

- Problems with the jaw, e.g., fracture or dislocation

- Radiation therapy

- Neurologic disorders such as myasthenia gravis, Parkinson's disease, multiple system atrophy, rabies, bulbar paralysis, bilateral facial nerve palsy, and hypoglossal nerve palsy

Generally, there is a good prognosis for low-grade tumors, and a poor prognosis for high-grade tumors.

Conditions that can cause saliva overproduction include:

- Rabies

- Pellagra (niacin or Vitamin B3 deficiency)

- Gastroesophageal reflux disease, in such cases specifically called a water brash, and is characterized by a sour fluid or almost tasteless saliva in the mouth

- Gastroparesis (main symptoms are nausea, vomiting, and reflux)

- Pregnancy

- Excessive starch intake

- Anxiety (common sign of separation anxiety in dogs)

- Pancreatitis

- Liver disease

- Serotonin syndrome

- Mouth ulcers

- Oral infections

Medications that can cause overproduction of saliva include:

- aripiprazole

- clozapine

- pilocarpine

- ketamine

- potassium chlorate

- risperidone

- rabeprazole sodium (Aciphex)

Toxins that can cause hypersalivation include:

- mercury

- copper

- organophosphates (insecticide)

- arsenic

Little is known about the total incidence of salivary gland tumours as most benign tumours go unrecorded in national cancer registries. The majority of salivary tumours are benign (65-70%). Within the parotid gland 75 - 80% of tumours are benign. Around 50% of the tumours found in the submandibular glands are benign. Sublingual gland tumours are very rare but if present, they are most likely to be malignant.

In the United States, salivary gland cancers are uncommon with an incidence rate of 1.7 in 100000 between 2009 and 2013.

Occurs in adults, with peak incidence from 20–40 years of age. A causal link with cytomegalovirus (CMV) has been strongly implicated in a 2011 research.

Most individuals come to clinical attention during the 5th decade, although the age range is broad (20 to 80 years). There is an equal gender distribution.

A sialocele is a localized, subcutaneous cavity containing saliva. It is caused by trauma (e.g. violence, accident or surgery) or infection. They most commonly develop about 8–14 days after injury.

They are a relatively common complication following surgery to the salivary glands, commonly parotidectomy (removal of the parotid gland). In this case the sialocele is the result of saliva draining out of remaining parotid tissue, and occurs about 5 to 10% of cases of superficial (partial) parotidectomy.

It is usually not painful, and a mild and self-limiting complication, and is managed by repeated aspiration (draining) of the swelling via a needle after the skin has been disinfected with an antibacterial. The fluid is usually a clear yellow, and contains amylase (in contrast to fluid from a seroma). Pressure dressings do not tend to be used. They are rarely chronic, however if persistent a surgical drain may be required. Botulinum toxin injections have also been used to manage this condition.