Sweat glands: structure and diseases

Sweat glands are tubular glands of the skin whose secretions are excreted to the surface or at the opening of a hair follicle. The general "architecture" of most types is similar: the secretory section is located deep in the dermis and/or subcutaneous tissue and is often coiled into a ball, while the excretory duct rises to the surface. [1]

Eccrine glands (often called "ordinary sweat glands") open directly onto the skin's surface through a pore. They produce a watery secretion that evaporates and cools the skin, making them a key tool for thermoregulation in humans, especially during physical exertion, heat, and fever. [2]

Apocrine glands are located primarily in the armpits, groin, and anogenital areas, around the areolae of the mammary glands, and in certain areas associated with hair follicles. Their secretion is initially more nutritious for skin bacteria, and the characteristic odor arises primarily from the bacterial breakdown of the secretion components. Therefore, apocrine glands are often discussed in the context of odor and inflammatory diseases in intertriginous areas. [3]

The secretory section of the sweat gland contains specialized cells that produce the secretion, and myoepithelial cells that help "squeeze" it into the duct. The excretory duct plays a separate role: it actively reabsorbs some electrolytes, which is why the resulting sweat is usually hypotonic compared to plasma, especially in heat-adapted individuals. [4]

Table 1. Eccrine and apocrine sweat glands: key differences [5]

Sign	Eccrine	Apocrine
Where does the duct open?	On the surface of the skin	Most often at the mouth of the hair follicle
Main function	Thermoregulation	Odor, “emotional” sweating, local effects in intertriginous areas
Type of secret	Water, electrolytes	More viscous, contains more organic components
Clinical associations	Hyperhidrosis, anhidrosis, miliaria	Hidradenitis suppurativa, bromhidrosis, some tumors of the skin appendages

Where are sweat glands located and why is their distribution uneven?

Sweat glands are distributed unevenly across the skin: they are abundant on the palms, soles, and armpits, while in some areas they are sparse or absent. This is because different areas of the skin serve different functions: in some areas, grip and traction are more important (palms and soles), in others, effective cooling, and in others, the signaling and "social" function of odor. [6]

Palmoplantar sweating is considered separately because it is often more closely associated with emotions and stress than with overheating. Moreover, due to the high density of eccrine glands in this area, hyperhidrosis can be particularly noticeable and socially significant, even at normal body temperature. [7]

Apocrine zones coincide with intertriginous areas, where friction, moisture, and dense microbiota exist. This creates conditions conducive to inflammatory processes when the barrier is compromised and the follicle is occluded. Therefore, painful nodules, abscesses, and fistulas associated with hidradenitis suppurativa are most common in the armpits, groin, and under the breasts. [8]

The "absence map" of glands is also important for clinical practice: certain mucocutaneous junctions and specialized areas of the skin may have a significantly lower density of sweat glands. This helps explain why complaints of sweating and irritation are concentrated in some areas and hardly affect others.

Table 2. Zones of high clinical significance of sweat glands [10]

Zone	Which glands are dominant?	Common problems
Palms and soles	Eccrine	Local hyperhidrosis, skin irritation, maceration
Armpits	Eccrine and apocrine	Axillary hyperhidrosis, bromhidrosis, hidradenitis suppurativa
Groin and perineum	Predominantly apocrine plus follicles	Hidradenitis suppurativa, irritation from friction and moisture
Torso	Eccrine	Miliaria with overheating and occlusion, generalized sweating with fever

How sweating is triggered and how sweat differs from "water"

Eccrine sweat glands receive sympathetic innervation, but the neurotransmitter most often is acetylcholine, which acts on muscarinic receptors and triggers secretion. The hypothalamus is considered the central "regulator" of thermoregulatory sweating, increasing or decreasing the activity of sympathetic fibers depending on core body temperature and external conditions. [11]

Sweating can be thermoregulatory or emotional. Emotional sweating is especially pronounced on the palms, soles, and sometimes in the armpits, which is why some people experience noticeable sweating without overheating due to stress and anxiety. This mechanism is important for understanding primary focal hyperhidrosis, which is characterized by "hyperreactivity" of sympathetic regulation. [12]

Sweat is primarily composed of water, but also electrolytes and small amounts of metabolites. A relatively "plasma-like" fluid is formed in the secretory compartment, and some of the sodium and chloride are reabsorbed in the duct. Therefore, the final sweat is usually less salty than plasma, and its "salinity" changes with adaptation to heat and in certain hereditary conditions. [13]

Contrary to popular myth, sweating is not the primary "detoxification" pathway. Urea and some salts are indeed eliminated through sweat, but the liver and kidneys play a leading role in removing metabolic products, while sweating is physiologically designed to cool and maintain a stable temperature. [14]

Table 3. Sweating regulation: quick reference points [15]

Trigger	Which areas react more strongly?	The main physiological meaning
Overheating, stress, fever	Torso, limbs	Evaporative cooling
Stress, anxiety, pain	Palms, soles, armpits	Emotional reaction, “preparation” for action
Acute hormonal reaction	Armpits and apocrine zones	Change in secretion, contribution to odor
Drugs and stimulants	Diverse	Side effect or increased sympathetic activity

Sweating disorders: hyperhidrosis, anhidrosis, miliaria, odor

Hyperhidrosis is sweating that objectively or subjectively exceeds thermoregulatory needs and interferes with daily life. It can be primary (usually focal, symmetrical, with onset in childhood or adolescence) or secondary, when sweating is associated with fever, endocrine disorders, medications, or other causes. [16]

A diagnostically important point: generalized night sweats, rapid onset of symptoms in adulthood, and pronounced systemic signs usually require a search for a secondary cause. Primary focal hyperhidrosis typically affects the palms, soles, armpits, and, less commonly, the face, with sweating often decreasing during sleep. [17]

Modern treatment for primary axillary hyperhidrosis is stepwise. Antiperspirants based on aluminum salts remain the basis, followed by topical anticholinergic agents, and, if ineffective, hardware-based treatments and injection therapy with botulinum toxin type A. Systemic anticholinergic drugs are used for some patients, but they are limited by side effects and contraindications. [18]

Important "new" developments include the availability of registered topical anticholinergic medications for axillary hyperhidrosis. For example, sofpironium (a topical antimuscarinic) was approved in the United States in 2024 for patients 9 years and older, reflecting a general trend toward topical therapy with less systemic burden. [19]

Anhidrosis and hypohidrosis are decreased sweating, which is primarily dangerous due to the risk of overheating and heatstroke. Causes include neuropathies, autonomic nervous system damage, certain medications, and extensive skin lesions with scarring. Miliaria (miliaria) develops when the excretory ducts become blocked and is most often associated with overheating, humidity, and skin occlusion. [20]

Table 4. Hyperhidrosis: primary and secondary [21]

Sign	Primary focal	Secondary
Start	Often in childhood or adolescence	Often in adulthood
Distribution	Focal, symmetrical	Often generalized
Night	Usually decreases	May persist
Tips	Stress, emotions, typical zones	Fever, weight loss, medications, endocrine symptoms

Table 5. Treatment of primary focal hyperhidrosis: step-by-step logic [22]

Step	Method	For which zones more often?	Practical limitations
1	Antiperspirants with aluminum salts	Armpits, palms, soles	Skin irritation, application regimen required
2	Local anticholinergic drugs	Armpits	Dry skin, possible anticholinergic effects if used incorrectly
3	Iontophoresis	Palms, soles	A course and supporting procedures are required
4	Botulinum toxin type A	Armpits, palms	Temporary effect, need for repetitions
5	Hardware methods and surgery	Armpits	The choice of method depends on availability and risks; specialist assessment is required.

Inflammatory diseases of the "apocrine zones" and tumors of the sweat glands

Hidradenitis suppurativa has historically been associated with apocrine glands, but a modern model views the disease as a chronic inflammatory disorder beginning with occlusion of the hair follicle, followed by immune mechanisms, abscesses, drainage tracts, and scarring. Clinically, the disease affects intertriginous areas: the armpits, groin, perianal region, and inframammary folds. [23]

In recent years, the approach to treating hidradenitis suppurativa has become more "immunological." European guidelines and reviews emphasize the role of biological agents in moderate to severe cases, including interleukin 17 blockade, as well as the need to combine systemic therapy with surgical methods for severe fistula tracts and scarring. [24]

Sweat gland tumors belong to a group of tumors of the skin appendages with eccrine and/or apocrine differentiation. They are rare, morphologically diverse, and sometimes mimic benign lesions or chronic inflammation, so diagnosis usually requires biopsy and pathological examination, often with immunohistochemistry and comparison with the World Health Organization classification. [25]

Malignant sweat gland tumors and cutaneous adnexal carcinomas are generally treated primarily surgically. Reviews emphasize that wide excision with controlled margins remains the standard, while Mohs micrographic surgery may be useful for reducing the risk of local recurrence in certain variants, particularly those with infiltrative growth and a tendency toward perineural invasion. [26]

A persistent nodule or ulcer in the sweat gland area is a specific warning sign, especially with repeated flare-ups in the same area, increasing pain, bleeding, numbness around the lesion, or suspected perineural spread. In such cases, early biopsy and referral to a dermatologist or onco-dermatologist are essential, as the rarity of these tumors does not protect against an aggressive course if diagnosed late. [27]

Table 6. Suppurative hidradenitis: clinical landmarks [28]

Sign	What it looks like in practice	What usually worsens the course
Deep painful nodes	Often in the armpits and groin	Friction, humidity, obesity, smoking
Abscesses and drainage	Purulent discharge, pain	Delayed treatment, repeated skin injuries
Fistula tracts	Chronic "tunnels" under the skin	Long-term inflammation without control
Scars and deformity	Compaction, retractions	Severe course and late therapy

Table 7. Sweat gland tumors and adnexal carcinomas: general principles [29]

Group	Example	The key problem	Basic tactics
Benign	Poroma, syringoma, hidradenoma	They look like "regular" knots	Removal according to indications, confirmation of morphology
Borderline and rare	Various variants with eccrine or apocrine differentiation	Risk of underestimation by type	Biopsy, clarification of diagnosis according to classification
Malignant	Porocarcinoma, hidradenocarcinoma and others	Relapses, metastases in some cases	Margin-controlled surgery, individual follow-up examination