Salivary gland cysts include salivary gland mucous cysts and parotid cysts, and salivary gland mucous cysts include minor salivary gland cysts and sublingual gland cysts. Mucous cysts can be divided into extravasation and retention depending on the etiology. Extravasation is more common, accounting for about 80% of cases, and is formed by rupture of the ducts with saliva leaking into the surrounding tissue spaces, caused by trauma; retention is less common, accounting for about 20% of cases, and is caused by partial obstruction of the ducts and cystic expansion of the ducts with saliva retention, so people with small or overly curved ducts are prone to suffer from cysts. Local inflammation can damage the duct opening and obstruct saliva secretion, which can easily lead to the development of the disease; people with too viscous saliva secretion have a higher risk of developing the disease; people with high calcium content in the saliva secretion can easily form small stones, which can block the ducts and are also prone to develop the disease; people with hyperactive salivary secretion, such as adolescents with well-developed salivary glands and high secretion, are also prone to develop the disease. Parotid cysts are classified into retention and congenital, while retention causes are the same as those of retention mucus cysts; congenital parotid cysts include dermatomal cysts, gill slit cysts and congenital ductal cystic dilatation, which are due to congenital developmental abnormalities.