Apocrine Glands

Apocrine glands, commonly called apocrine sweat glands, are large coiled tubular glands associated with the skin. Unlike eccrine sweat glands, which are widely distributed over the body surface, apocrine glands are concentrated in specific regions, particularly the axillae, areolae, and anogenital region.

Apocrine glands are usually associated with hair follicles. Their ducts generally empty into the upper portion of a hair follicle rather than opening directly onto the skin surface. They become functionally active around puberty and produce a relatively viscous secretion containing proteins, lipids, and other organic substances.

The secretion is initially largely odorless. Characteristic body odor develops mainly after components of the secretion are metabolized by microorganisms living on the skin.

Classification

Apocrine glands are classified as specialized simple coiled tubular glands. Each gland consists of a secretory portion and a duct that carries the glandular product toward a hair follicle.

Location

Apocrine glands have a restricted distribution compared with eccrine glands. They are particularly prominent in the axillary and anogenital regions and around the nipple and areola.

Major Sites

Region	Apocrine Gland Distribution
Axilla	Abundant
Areola	Present
Anogenital region	Present
Most general skin	Sparse or absent
Palms and soles	Absent

Position Within the Skin

The secretory portions of apocrine glands lie relatively deep within the skin, typically in the deep dermis or subcutaneous tissue.

The duct travels toward the associated pilosebaceous unit and usually opens into the hair follicle.

Relationship to Hair Follicles

Apocrine glands are anatomically associated with hair follicles. This relationship distinguishes them from typical eccrine glands, whose ducts open independently onto the epidermal surface.

The apocrine duct generally enters the follicular canal superficial to the opening of the sebaceous gland.

Pilosebaceous and Apocrine Relationship

Structure	Relationship
Hair follicle	Receives the duct of a typical apocrine gland
Sebaceous gland	Also empties into the follicle, generally at a deeper level
Apocrine gland	Secretory coil lies deep and connects to follicle by a duct
Epidermal surface	Usually reached indirectly through the hair follicle

Secretory Portion

The secretory component is a coiled tubular structure with a characteristically wide lumen. It is generally larger than the secretory portion of an eccrine sweat gland.

The secretory epithelium is composed of cuboidal to columnar cells whose appearance varies with functional activity.

Secretory Cells

Secretory cells produce the glandular fluid released into the lumen. Their cytoplasm contains organelles associated with synthesis and secretion of proteins and other components.

The apical surface of the cells may show protrusions into the lumen, a feature historically associated with the term apocrine secretion.

Myoepithelial Cells

Myoepithelial cells are located between the secretory epithelial cells and the basement membrane. These contractile cells help expel secretory material from the glandular lumen into the duct.

Apocrine Duct

The duct is narrower than the secretory portion and is lined by stratified cuboidal epithelium. It conveys secretion toward the associated hair follicle.

Secretory Portion Versus Duct

Feature	Secretory Portion	Duct
Lumen	Relatively wide	Narrower
Epithelium	Usually cuboidal to columnar secretory cells	Usually stratified cuboidal
Myoepithelial cells	Present	Not a prominent feature of the duct
Primary role	Produces secretion	Conducts secretion

Histological Appearance

In histological sections, apocrine glands appear as coiled tubular profiles within the deep dermis or subcutaneous tissue. Their large lumina are an important identifying feature.

Multiple cross-sections of the same coiled gland may appear near one another within a tissue section.

Histological Identification

Feature	Typical Appearance
Location	Deep dermis or hypodermis
Gland type	Coiled tubular gland
Lumen	Large and conspicuous
Secretory epithelium	Cuboidal to columnar
Myoepithelial cells	Located around secretory epithelium
Duct	Stratified cuboidal epithelium

Apocrine Secretion

The secretion of apocrine glands is more viscous and contains more organic material than typical eccrine sweat. Components include proteins, lipids, and other substances.

Despite the historical terminology, human apocrine sweat glands use secretory mechanisms that include exocytosis, and the name should not be interpreted as meaning that all secretion occurs by loss of the apical cytoplasm.

Why They Are Called Apocrine Glands

The term apocrine originated from the observation of apical protrusions or apparent decapitation-like changes in secretory cells.

Modern understanding of their secretion is more complex, and the anatomical name has persisted even though the classical apocrine mechanism does not fully describe all secretory activity of these glands.

Composition of Secretion

Apocrine gland secretions contain water along with proteins, lipids, electrolytes, and other organic compounds. The exact composition varies with gland activity and anatomical location.

Body Odor

Fresh apocrine secretion is not responsible for strong odor by itself. Characteristic body odor develops when skin microorganisms metabolize components of the secretion and generate volatile compounds.

Relationship to Skin Microbiota

The axilla contains a specialized microbial environment. Bacterial metabolism of apocrine-derived molecules contributes substantially to the characteristic odor associated with this region.

Activation at Puberty

Apocrine glands become functionally prominent around puberty. Their maturation and activity are associated with hormonal changes occurring during sexual development.

Hormonal Influence

The development and activity of apocrine glands are influenced by hormonal factors. This distinguishes their life-course pattern from eccrine glands, which function much earlier in life.

Innervation

Apocrine glands are influenced by autonomic nervous activity. Emotional and sensory stimuli can promote secretion, particularly in regions such as the axilla.

Emotional Sweating

Apocrine activity may increase during emotional stress, excitement, pain, or other stimuli. However, the large-scale production of watery sweat for thermoregulation is primarily a function of eccrine glands.

Role in Thermoregulation

Apocrine glands have only a limited role in human thermoregulation. Eccrine sweat glands are the major glands responsible for evaporative cooling.

Apocrine Versus Eccrine Glands

Feature	Apocrine Gland	Eccrine Gland
Distribution	Restricted to selected regions	Widely distributed
Typical opening	Hair follicle	Directly onto skin surface
Secretory lumen	Large	Smaller
Secretion	More viscous and rich in organic compounds	Predominantly watery
Functional activity	Becomes prominent at puberty	Functional much earlier
Thermoregulation	Minor role	Major role
Association with hair	Usually present	Not required

Apocrine Versus Sebaceous Glands

Feature	Apocrine Gland	Sebaceous Gland
Gland type	Coiled tubular	Branched acinar or alveolar
Product	Protein- and lipid-containing fluid	Sebum
Typical opening	Hair follicle	Hair follicle
Secretory process	Primarily secretory release from viable cells	Holocrine
Location of secretory unit	Deep dermis or hypodermis	Usually more superficial in dermis

Specialized Apocrine Glands

Certain glands in specialized anatomical regions are considered modified apocrine glands or share important structural features with apocrine glands.

Ceruminous Glands

Ceruminous glands of the external acoustic meatus are modified apocrine glands. Their secretions contribute, together with sebaceous gland products and desquamated cells, to the formation of cerumen.

Mammary Glands

The mammary glands are highly specialized cutaneous glands with developmental and secretory relationships to apocrine-type glands. Their structure becomes extensively modified for milk production.

Glands of Moll

The glands of Moll are modified apocrine glands located at the eyelid margin and associated with eyelashes.

Specialized Apocrine-Type Glands

Gland	Location or Function
Ceruminous glands	External acoustic meatus, contribute to cerumen
Glands of Moll	Eyelid margin
Mammary glands	Highly specialized glands for milk production

Development

Apocrine glands develop as epithelial downgrowths associated with developing hair follicles. Their anatomical relationship with the follicular unit is therefore established during development.

Relationship to the Pilosebaceous Unit

A typical apocrine gland participates in a broader anatomical complex that includes the hair follicle and sebaceous gland.

This close relationship is clinically important because inflammatory disorders may involve several components of the follicular and apocrine-bearing region simultaneously.

Hidradenitis Suppurativa

Hidradenitis suppurativa is a chronic inflammatory disorder affecting hair follicle-bearing intertriginous skin, commonly including the axillae and groin.

Although historically described as a disorder of apocrine glands, current understanding places follicular occlusion and rupture at the center of its pathogenesis, with secondary involvement of surrounding structures, including apocrine glands.

Common Sites of Hidradenitis Suppurativa

Site	Characteristic
Axilla	Commonly affected
Groin	Commonly affected
Perineal and perianal regions	May be affected
Inframammary region	May be affected

Apocrine Hidrocystoma

An apocrine hidrocystoma is a benign cystic lesion showing apocrine differentiation. Histological examination may demonstrate a cystic space lined by epithelial cells with apocrine-type features.

Apocrine Neoplasms

Benign and malignant tumors with apocrine differentiation can occur in the skin. Their diagnosis depends on microscopic architecture, cytological features, immunohistochemistry, and clinical context.

Axillary Anatomy

The axilla contains a high concentration of apocrine glands associated with terminal hair follicles. The warm, relatively occluded environment also supports bacterial metabolism of glandular secretions.

This combination makes the axilla the region most strongly associated with apocrine-derived body odor.

Anogenital Apocrine Glands

Apocrine glands are present in parts of the anogenital region, where they are associated with hair-bearing skin and contribute to the specialized glandular anatomy of the region.

Areolar Glands

Apocrine-type glands occur in association with the areolar region of the breast. The skin of the nipple and areola contains several specialized glandular structures.

Clinical Identification

In pathology specimens, the combination of a large tubular lumen, secretory epithelial lining, and apical cytoplasmic protrusions can suggest apocrine differentiation.

Interpretation requires consideration of anatomical site and surrounding structures because several cutaneous lesions can display apocrine-like morphology.

Functions of Apocrine Glands

Function or Feature	Role
Regional secretion	Produces a viscous secretion in selected hair-bearing regions
Follicular delivery	Secretion usually enters a hair follicle
Odor precursor production	Provides compounds metabolized by skin microorganisms
Response to emotional stimuli	Secretory activity can increase with autonomic stimulation
Specialized gland development	Related glandular structures are modified for specialized regional functions

Key Features of Apocrine Glands

Feature	Key Point
Gland type	Large simple coiled tubular gland
Main distribution	Axillae, areolae, and anogenital region
Depth	Deep dermis and subcutaneous tissue
Typical duct opening	Hair follicle
Secretory lumen	Relatively large
Secretory cells	Cuboidal to columnar
Myoepithelial cells	Surround secretory units and aid expulsion
Activity	Becomes prominent around puberty
Thermoregulatory role	Limited
Odor	Develops mainly through bacterial modification of secretions

Anatomical and Functional Importance

Apocrine glands are specialized skin appendages adapted for regional secretion rather than whole-body thermoregulation. Their restricted distribution and close association with hair follicles distinguish them anatomically from the widely distributed eccrine sweat glands.

Their large secretory coils lie deep within the skin and are surrounded by contractile myoepithelial cells. Secretory products pass through ducts into hair follicles and eventually reach the skin surface.

The interaction between apocrine secretions and the cutaneous microbiota is responsible for much of the characteristic odor associated with apocrine-rich regions, particularly the axilla.

Apocrine glands are also clinically important because their anatomical regions are involved in disorders such as hidradenitis suppurativa and in several benign and malignant lesions showing apocrine differentiation. They therefore provide an important link between skin appendage anatomy, hair follicles, glandular histology, regional secretion, microbiology, and clinical dermatology.