Hyperplasia is considered to be a physiological (normal) response to a specific stimulus, and the cells of a hyperplastic growth remain subject to normal regulatory control mechanisms. However, hyperplasia can also occur as a pathological response, if an excess of hormone or growth factor is responsible for the stimuli. Similarly to physiological hyperplasia, cells that undergo pathologic hyperplasia are controlled by growth hormones, and cease to proliferate if such stimuli are removed. This differs from neoplasia (the process underlying cancer and benign tumors), in which genetically abnormal cells manage to proliferate in a non-physiological manner which is unresponsive to normal stimuli. That being said, the effects caused by pathologic hyperplasia can provide a suitable foundation from which neoplastic cells may develop.

Hyperplasia (from ancient Greek ὑπέρ "huper", "over" + πλάσις "plasis", "formation"), or hypergenesis, is an increase in the amount of organic tissue that results from cell proliferation. It may lead to the gross enlargement of an organ and the term is sometimes confused with benign neoplasia or benign tumor.

Hyperplasia is a common preneoplastic response to stimulus. Microscopically, cells resemble normal cells but are increased in numbers. Sometimes cells may also be increased in size (hypertrophy). Hyperplasia is different from hypertrophy in that the adaptive cell change in hypertrophy is an increase in the "size" of cells, whereas hyperplasia involves an increase in the "number" of cells.

Generalized trichoepitheliomas are characterized histologically by replacement of the hair follicles by trichoepithelioma-like epithelial proliferations associated with hyperplastic sebaceous glands.

Hidrocystoma (also known as cystadenoma, a Moll's gland cyst, and a sudoriferous cyst) is an adenoma of the sweat glands.

Hidrocystomas are cysts of sweat ducts, usually on the eyelids. They are not tumours (a similar-sounding lesion called hidroadenoma is a benign tumour).

There are three types of "sweat" glands: True sweat glands or eccrine glands;

sebaceous glands, which have an oily secretion around hair follicles; and apocrine glands which have more oily product than eccrine glands and are found on the face, armpit, and groin.

Hidrocystomas usually arise from apocrine glands. They are also called Cysts of Moll or sudoriferous cysts. There may be a type of hidroadenoma that arises from eccrine glands, but these are uncommon.

Other related conditions on the eyelids include chalazion ( a granulomatous reaction to sebaceous glands on the eyelid), lacrimal duct cysts (cysts related to tear ducts) and nasolacrimal duct cysts (the nasolacrimal duct drains tears into the nose via a punctum on the lower eyelid).

A sebaceous adenoma, a type of adenoma, a cutaneous condition characterized by a slow-growing tumor usually presenting as a pink, flesh-coloured, or yellow papule or nodule.

Nevus sebaceus or sebaceous nevus (the first term is its Latin name, the second term is its name in English; also known as an "organoid nevus" and "nevus sebaceus of Jadassohn") is a congenital, hairless plaque that typically occurs on the face or scalp. Such nevi are present at birth, or early childhood, affecting males and females of all races equally. The condition is named for an overgrowth of sebaceous glands in the area of the nevus.

Skin growths such as benign tumors and basal cell carcinoma can arise in sebaceous nevi, usually in adulthood. Rarely, sebaceous nevi can give rise to sebaceous carcinoma. However, the rate of such malignancies is now known to be less than had been estimated. For this reason, excision is no longer automatically recommended.

Blepharophyma is chronic swelling of eyelids, mainly due to sebaceous gland hyperplasia.

Infants born with congenital hypothyroidism may show no effects, or may display mild effects that often go unrecognized as a problem: excessive sleeping, reduced interest in nursing, poor muscle tone, low or hoarse cry, infrequent bowel movements, exaggerated jaundice, and low body temperature. If fetal deficiency was severe because of complete absence (athyreosis) of the gland, physical features may include a larger anterior fontanel, persistence of a posterior fontanel, an umbilical hernia, and a large tongue (macroglossia).

In the era before newborn screening, less than half of cases of severe hypothyroidism were recognized in the first month of life. As the months proceeded, these babies would grow poorly and be delayed in their development. By several years of age, they would display the recognizable facial and body features of cretinism. Persistence of severe, untreated hypothyroidism resulted in severe mental impairment, with an IQ below 80 in the majority. Most of these children eventually ended up in institutional care.

An adenoma of a parathyroid gland may secrete inappropriately high amounts of parathyroid hormone and thereby cause primary hyperparathyroidism.

Adnexal and skin appendage neoplasms is a group of tumors which develop in the adnexal skin structures such as the sweat and sebaceous glands. An example is the hidrocystoma.

Sebaceous hyperplasia is a disorder of the sebaceous glands in which they become enlarged, producing flesh-colored or yellowish, shiny, often umbilicated bumps on the face. Newly formed nodules often swell with sweating (which is pathognomonic for the condition), but this diminishes over time.

Sebaceous glands are glands located within the skin and are responsible for secreting an oily substance named sebum. They are commonly associated with hair follicles but they can be found in hairless regions of the skin as well. Their secretion lubricates the skin, protecting it from drying out or becoming irritated.

Sebaceous hyperplasia generally affects newborns as well as middle-aged to elderly adults. The symptoms of this condition are 1–5 mm papules on the skin, mainly on the forehead, nose and cheeks, and seborrheic facial skin. The papules may be cauliflower-shaped. In infants, acne is sometimes associated with sebaceous hyperplasia.

See Hepatocellular adenoma. Hepatic adenomas are a rare benign tumour of the liver, which may present with hepatomegaly or other symptoms.

On the shaft of the penis, Fordyce spots are more visible when the skin is stretched, and may only be noticeable during an erection.

The spots can also appear on the skin of the scrotum.

Oral Fordyce granules appear as rice-like granules, white or yellow-white in color. They are painless papules (small bumps), about 1–3 mm in greatest dimension. The most common site is along the line between the vermilion border and the oral mucosa of the upper lip, or on the buccal mucosa (inside the cheeks) in the commissural region, often bilaterally. They may also occur on the mandibular retromolar pad and tonsillar areas, but any oral surface may be involved. There is no surrounding mucosal change. Some patients will have hundreds of granules while most have only one or two.

Occasionally, several adjacent glands will coalesce into a larger cauliflower-like cluster similar to sebaceous hyperplasia of the skin. In such an instance, it may be difficult to determine whether or not to diagnose the lesion as sebaceous hyperplasia or sebaceous adenoma. The distinction may be moot because both entities have the same treatment, although the adenoma has a greater growth potential. Sebaceous carcinoma of the oral cavity has been reported, presumably arising from Fordyce granules or hyperplastic foci of sebaceous glands.

In some persons with Fordyce spots, the glands express a thick, chalky discharge when squeezed.

Sebaceous adenomas, in isolation, are not significant; however, they may be associated with Muir-Torre syndrome, a genetic condition that predisposes individuals to cancer. It is also linked to hereditary nonpolyposis colorectal cancer (Lynch Syndrome).

It is not the same as "adenoma sebaceum" by F. Balzer and P.E. Ménétrier (1885). The term "adenoma sebaceum" is a misnomer for "facial angiofibromas" associated with tuberous sclerosis complex.

Sebaceous glands are normal structures of the skin but may also be found ectopically in the mouth, where they are referred to as "oral Fordyce granules" or ectopic sebaceous glands.

On the foreskin they are called Tyson's glands, not to be confused with hirsuties coronae glandis.

When they appear on the penis, they are also called "penile sebaceous glands".

When seen as a streak of individual glands along the interface between the skin of the lip and the vermilion border, the terms Fox–Fordyce disease and Fordyce's condition have been used.

Congenital hypothyroidism (CH) is a condition of thyroid hormone deficiency present at birth. Approximately 1 in 4000 newborn babies has a severe deficiency of thyroid function, while even more have mild or partial degrees. If untreated for several months after birth, severe congenital hypothyroidism can lead to growth failure and permanent intellectual disability. Treatment consists of a daily dose of thyroid hormone (thyroxine) by mouth. Because the treatment is simple, effective, and inexpensive, nearly all of the developed world practices newborn screening to detect and treat congenital hypothyroidism in the first weeks of life.

Since the original identification of Schimmelpenning syndrome, the number of findings has expanded to the point that the syndrome is associated with a considerable constellation of abnormalities. The abnormalities may occur in a variety of combinations, and need not include all three aspects of the classic triad of sebaceous nevus, seizures and mental retardation. In 1998, a literature review by van de Warrenburg et al. found:

- seizures in 67% of cases

- mental retardation in 61% of cases

- ophthalmological abnormalities in 59% of cases

- involvement of other organ systems in 61% of cases

- structural abnormality of cerebrum or cranium in 72% of cases

The major neurological abnormalities include mental retardation to varying extent, seizures, and hemiparesis. Seizures, when present, typically begin during the first year of life. The most common structural central nervous system abnormalities in Schimmelpenning syndrome are hemimegalencephaly and ipselateral gyral malformations.

The major ocular abnormalities are colobomas and choristomas.

Skeletal abnormalities may include dental irregularities, scoliosis, vitamin D-resistant rickets and hypophosphatemia. Cardiovascular abnormalities include ventricular septal defect and co-arctation of the aorta; urinary system issues include horseshoe kidney and duplicated urinary collection system.

The treatment is simple excision and exclusion of a malignant neoplasm.

Sebaceous lymphadenoma is a tissue diagnosis, e.g. salivary gland biopsy.

It may be confused with a number of benign and malignant neoplasms, including Warthin tumour, mucoepidermoid carcinoma and sebaceous lymphadenocarcinoma.

Folliculosebaceous cystic hamartoma abbreviated as (FSCH) is a rare cutaneous hamartoma consisting of dilated folliculosebaceous units invested in mesenchymal elements. it typically affects adults, have a predilection for the central face or scalp, with less than 1.5 cm dimension. Clinically, the lesions are asymptomatic, rubbery to firm in consistency, and usually occur on or above the neck in (> 90%) of cases, Histopathologically, FSCH shares several similar features to sebaceous trichofolliculoma, but it is usually possible to differentiate these two tumors.

Additional types of nevi do not involve disorders of pigmentation or melanocytes. These additional nevi represent hamartomatous proliferations of the epithelium, connective tissue, and vascular malformations.

Salivary gland tumours usually present as a lump or swelling in the affected gland which may or may not have been present for a long time. The lump may be accompanied by symptoms of duct blockage (e.g. xerostomia). Usually, in their early stages it is not possible to distinguish a benign tumour from a malignant one. One of the key differentiating symptoms of a malignant growth is nerve involvement. For example signs of facial nerve damage (e.g facial palsy) are associated with malignant parotid tumours. Facial pain, and paraesthesia are also very often associated with a malignant tumours. Other red flag symptoms which may suggest malignancy and warrant further investigation are fixation of the lump to the overlying skin, ulceration and induration of the mucosa.

The term "nevus" is applied to a number of conditions caused by neoplasias and hyperplasias of melanocytes, as well as a number of pigmentation disorders, both hypermelanotic (containing increased melanin, the pigment responsible for skin color) and hypomelanotic (containing decreased melanin).

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.

Schimmelpenning syndrome is a neurocutaneous condition characterized by one or more sebaceous nevi, usually appearing on the face or scalp, associated with anomalies of the central nervous system, ocular system, skeletal system, cardiovascular system, and genitourinary system.

Synonyms include: "Linear nevus sebaceous syndrome (LNSS)", "Schimmelpenning-Feuerstein-Mims syndrome", "Feuerstein-Mims syndrome", "sebaceous nevus syndrome", "Solomon syndrome", and "Jadassohn's nevus phakomatosis". "Nevus" is sometimes spelled "naevus" and "sebaceous" may also be spelled "sebaceus". "Epidermal nevus syndrome" is sometimes used as a synonym, but more often as a broader term referring to Schimmelpenning syndrome in addition to nevus comedonicus syndrome, CHILD syndrome, Becker's nevus syndrome, and phakomatosis pigmentokeratotica.

The classic Schimmelpenning syndrome diagnosis comprises a triad of sebaceous nevi, seizures, and mental retardation. The condition was first reported by Gustav Schimmelpenning in 1957 and independently reported by Feuerstein and Mims in 1962.