Most commonly affects women aged 13–35 years, approximately puberty through their prime. Some reports show affected women to men at 9:1. Rare cases have been shown to affect post-menopausal women, children, and men. Incident report is currently unknown. Although rare, men and children have been shown to be affected. Heat, humidity, stress, and exercise have been shown to worsen symptoms. Rate of incidence is currently unknown. Fox-Fordyce has also been shown to be severe during menstruation and spontaneously disappear during pregnancy

Exact cause of Fox-Fordyce is currently unknown. Studies have not been able to confirm if apocrine gland duct obstruction is required for development. It is speculated that gland duct rupture causes inflammation. Inflammatory response includes white blood cells.

The overwhelming majority of reported AIGA patients are Japanese, but whether AIGA is truly rare in whites or has been simply underreported by Western physicians remains unclear.

AIGA is most prevalent among young men. In a 64 case review of the literature 58 reported cases were males and 6 female, with a mean age of onset at 28 ± 11 years. Cholinergic urticaria or sharp pain over the entire body induced by elevated body temperature was reported in 32 cases (50%). Of 28 cases tested, 12 (43%) displayed elevated serum IgE levels. Skin biopsy was performed in 53 cases, with normal findings in 20 cases (38%), and cellular infiltrates in sweat glands or ducts in 23 cases (43%).

Several triggering factors should be taken into consideration:

- Obesity is an exacerbating rather than a triggering factor, through mechanical irritation, occlusion, and maceration.

- Tight clothing, and clothing made of heavy, non-breathable materials.

- Deodorants, depilation products, shaving of the affected area – their association with hidradenitis suppurativa is still an ongoing debate amongst researchers.

- Drugs, in particular oral contraceptives (i.e., oral hormonal birth control; "the pill") and lithium.

- Hot and especially humid climates (dry/arid climates often cause remission).

Hyperthyroidism is a state in which the body is producing too much thyroid hormone. The main hyperthyroid conditions are:

- Graves' disease

- Toxic thyroid nodule

- Thyroid storm

- Toxic nodular struma (Plummer's disease)

- Hashitoxicosis: "transient" hyperthyroidism that can occur in Hashimoto's thyroiditis

Intracutaneous injection of pilocarpine (sweat gland stimulant) is known to evoke no sweat response, indicating that lesions are on the post-synaptic side of the nerve-sweat gland junction.

The proposed pathomechanisms of idiopathic pure sudomotor failure include:

- A deficit within muscarinic cholinergic receptors of the eccrine sweat glands.

- Interference in acetylcholine transmission to cholinergic receptors.

- A cross-reactive immune response which interferes with cholinergic transmission in the eccrine glands.

- Components of an immediate-type allergy (based on the dramatic resumption of axon reflex sweating following glucocorticoid treatment).

Hypothyroidism is a state in which the body is not producing enough thyroid hormones, or is not able to respond to / utilize existing thyroid hormones properly. The main categories are:

- Thyroiditis: an inflammation of the thyroid gland

- Hashimoto's thyroiditis / Hashimoto's disease

- Ord's thyroiditis

- Postpartum thyroiditis

- Silent thyroiditis

- Acute thyroiditis

- Riedel's thyroiditis (the majority of cases do not affect thyroid function, but approximately 30% of cases lead to hypothyroidism)

- Iatrogenic hypothyroidism

- Postoperative hypothyroidism

- Medication- or radiation-induced hypothyroidism

- Thyroid hormone resistance

- Euthyroid sick syndrome

- Congenital hypothyroidism: a deficiency of thyroid hormone from birth, which untreated can lead to cretinism

In stage III disease, fistulae left undiscovered, undiagnosed, or untreated, can lead to the development of squamous cell carcinoma, a rare cancer, in the anus or other affected areas. Other stage III chronic sequelae may also include anemia, multilocalized infections, amyloidosis, and arthropathy. Stage III complications have been known to lead to sepsis, but clinical data is still uncertain.

Hidradenitis is any disease in which the histologic abnormality is primarily an inflammatory infiltrate around the eccrine glands. This group includes neutrophilic eccrine hidradenitis and recurrent palmoplantar hidradenitis.

It can also be defined more generally as an inflammation of sweat glands.

Hidradenitis suppurativa is a chronic cutaneous condition originally thought to be primarily characterized by suppurative inflammation of the apocrine sweat glands. However, recent evidence supports that the primary event is follicular hyperkeratosis and obstruction.

Chromhidrosis (also referred to as "colored sweat") is a rare condition characterized by the secretion of colored sweat. It is caused by the deposition of lipofuscin in the sweat glands. Cases of red, blue, green, yellow, pink, and black sweat have been reported. Usually chromhidrosis affects the apocrine glands, mainly on the face and underarms. A limited number of treatment options exist, including regular application of Capsaicin cream and prolonged relief may be provided by botulinum toxin treatment. Chromogenic pigments produced by bacteria ("Corynebacterium" in particular) are implicated in this condition but their exact role still requires careful microbiological elucidation. Chromhidrosis of the eccrine glands is rare, it occurs mainly after the ingestion of certain dyes or drugs.

Hidradenitis suppurativa is a chronic inflammatory skin condition, considered a member of the acne family of disorders. It is sometimes called acne inversa. The first signs of HS are small bumps on the skin that resemble pimples, cysts, boils, or folliculitis. As the disease progresses and abscesses reoccur, they become larger and more painful; eventually tunnels of scar tissue connect the lesions. These lesions may open up if they become too enlarged and drain bloodstained pus. One risk factor is age; HS usually first appears during the 20s and early 30s. The condition is much more common in women than in men but is usually more serious and debilitating in men. Other associated conditions include obesity, diabetes, metabolic syndrome, arthritis, acne, and other inflammatory disorders. Early diagnosis of this disease is very important to decrease the number of flares, pain, and discomfort.

Most types of thyroiditis are three to five times more likely to be found in women than in men. The average age of onset is between thirty and fifty years of age. This disease tends to be geographical and seasonal, and is most common in summer and fall.

An Apocrine nevus is an extremely rare cutaneous condition that is composed of hyperplastic mature apocrine glands.

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).

Thyroiditis is generally caused by an attack on the thyroid, resulting in inflammation and damage to the thyroid cells. This disease is often considered a malfunction of the immune system. Antibodies that attack the thyroid are what causes most types of thyroiditis. It can also be caused by an infection, like a virus or bacteria, which works in the same way as antibodies to cause inflammation in the glands. Certain people make thyroid antibodies, and thyroiditis can be considered an autoimmune disease, because the body acts as if the thyroid gland is foreign tissue. Some drugs, such as interferon and amiodarone, can also cause thyroiditis because they have a tendency to damage thyroid cells.

"Dehydration:"

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

Hyperthyroidism is very rare in dogs, occurring in less than 1% of dogs. Hyperthyroidism may be caused by a thyroid tumor. This may be a thyroid carcinoma. About 90% of carcinomas are a very aggressive; they invade the surrounding tissues and metastasize (spread), to other tissues, particularly the lungs. This has a poor prognosis. Surgery to remove the tumor a carcinoma is often very difficult, due to the spread of the tumor to the surrounding tissue, for example, into arteries, the esophagus, or the windpipe. It may be possible to reduce the size of the tumor, thus relieving symptoms and allowing time for other treatments to work. About 10% of thyroid tumors are benign; these often cause few symptoms.

In dogs treated for hypothyroidism (lack of thyroid hormone), hyperthyroidism may occur as a result of an overdose of the thyroid hormone replacement medication, levothyroxine; in this case treatment involves reducing the dose of levothyroxine. Dogs which display coprophagy, that is, which often eat feces, and which live in a household with a dog receiving levothyroxine treatment, may develop hyperthryoidism if they frequently eat the feces from the dog receiving levothyroxine treatment.

Hyperthyroidism may occur if a dog eats an excessive amount of thyroid gland tissue. This has occurred in dogs fed commercial dog food.

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.

There are several causes of hyperthyroidism. Most often, the entire gland is overproducing thyroid hormone. Less commonly, a single nodule is responsible for the excess hormone secretion, called a "hot" nodule. Thyroiditis (inflammation of the thyroid) can also cause hyperthyroidism. Functional thyroid tissue producing an excess of thyroid hormone occurs in a number of clinical conditions.

The major causes in humans are:

- Graves' disease. An autoimmune disease (usually, the most common etiology with 50-80% worldwide, although this varies substantially with location- i.e., 47% in Switzerland (Horst et al., 1987) to 90% in the USA (Hamburger et al. 1981)). Thought to be due to varying levels of iodine in the diet. It is eight times more common in females than males and often occurs in young females, around 20 – 40 years of age.

- Toxic thyroid adenoma (the most common etiology in Switzerland, 53%, thought to be atypical due to a low level of dietary iodine in this country)

- Toxic multinodular goiter

High blood levels of thyroid hormones (most accurately termed hyperthyroxinemia) can occur for a number of other reasons:

- Inflammation of the thyroid is called thyroiditis. There are several different kinds of thyroiditis including Hashimoto's thyroiditis (Hypothyroidism immune-mediated), and subacute thyroiditis (de Quervain's). These may be "initially" associated with secretion of excess thyroid hormone but usually progress to gland dysfunction and, thus, to hormone deficiency and hypothyroidism.

- Oral consumption of excess thyroid hormone tablets is possible (surreptitious use of thyroid hormone), as is the rare event of consumption of ground beef contaminated with thyroid tissue, and thus thyroid hormone (termed "hamburger hyperthyroidism").

- Amiodarone, an antiarrhythmic drug, is structurally similar to thyroxine and may cause either under- or overactivity of the thyroid.

- Postpartum thyroiditis (PPT) occurs in about 7% of women during the year after they give birth. PPT typically has several phases, the first of which is hyperthyroidism. This form of hyperthyroidism usually corrects itself within weeks or months without the need for treatment.

- A struma ovarii is a rare form of monodermal teratoma that contains mostly thyroid tissue, which leads to hyperthyroidism.

- Excess iodine consumption notably from algae such as kelp.

Thyrotoxicosis can also occur after taking too much thyroid hormone in the form of supplements, such as levothyroxine (a phenomenon known as exogenous thyrotoxicosis, alimentary thyrotoxicosis, or occult factitial thyrotoxicosis).

Hypersecretion of thyroid stimulating hormone (TSH), which in turn is almost always caused by a pituitary adenoma, accounts for much less than 1 percent of hyperthyroidism cases.

A folliculosebaceous-apocrine hamartoma, also known as "follicular-apocrine hamartoma", is a benign proliferation of the folliculosebaceous-apocrine unit.

"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.

Papillary eccrine adenoma (also known as "tubular apocrine adenoma") is a cutaneous condition characterized by an uncommon benign sweat gland neoplasm that presents as a dermal nodule located primarily on the extremities of black patients.

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).

The prevalence and incidence of Grover's disease have not been firmly established. In a study from Switzerland, Grover's disease was diagnosed in just 24 of more than 30,000 skin biopsies [4]. Grover's disease is mainly seen in males over the age of forty.

Grover's disease affects chiefly white adults in the fifth decade or later, and appears to be around 1.6 to 2.1 times more common in men than in women. Grover's disease appears less commonly in darker-skinned individuals.

Apocrine gland carcinoma is a cutaneous condition characterized by skin lesions which form in the axilla or anogenital regions.