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Skin appendage
Skin appendage
Skin appendage
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Skin appendages
Details
SystemIntegumentary system
Identifiers
Latinadnexa cutis
THH3.12.00.3.00001
FMA71012
Anatomical terminology

Skin appendages (or adnexa of skin) are anatomical skin-associated structures that serve a particular function including sensation, contractility, lubrication and heat loss in animals. In humans, some of the more common skin appendages are hairs (sensation, heat loss, filter for breathing, protection), arrector pilli (smooth muscles that pull hairs straight), sebaceous glands (secrete sebum onto hair follicle, which oils the hair), sweat glands (can secrete sweat with strong odour (apocrine) or with a faint odour (merocrine or eccrine), and nails (protection).

Skin appendages are derived from the skin, and are usually adjacent to it.[1]

Glands

[edit]
  • Sweat glands are distributed all over the body except nipples and outer genitals. Although the nipples do have the mammary glands, these are known as modified sweat glands.
  • Sebaceous glands are typically found in the opening shafts of hair. They are not on the palms of the hands or the soles of the feet. These glands secrete an antibacterial moisture known as sebum fluid. The sebum also softens the hands. The secretion activity is related to hormonal release. If acne is occurring, it is because these gland ducts are blocked.
  • Eccrine (merocrine) glands are most common. The secretions are very watery that contain some electrolytes
  • Apocrine glands produce a fatty secretion, thus giving away an odorous smell. These are located in the inguinal and axillary regions of the body, and include the mammary glands.

References

[edit]
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Skin appendage

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Skin appendages, also known as adnexa of the skin, are specialized epithelial structures that develop from the and extend into the , primarily including , , sebaceous glands, and sweat glands. These appendages are integral components of the , forming pilosebaceous units (hair follicles associated with sebaceous glands) and contributing to the skin's overall functionality across the body's surface area of approximately 2 square meters in adults. Hair consists of a visible shaft emerging from a follicle rooted in the , with a bulb at the base containing the growth matrix; it is composed primarily of and is present on most body surfaces except glabrous areas like palms and soles. Nails feature a hard keratinized plate overlying the nail bed, with growth originating from the proximal matrix and a characteristic white lunula at the base, serving to protect the distal digits. Sebaceous glands, structures embedded in the , secrete sebum—an oily, waxy substance that lubricates the skin and hair while providing and photoprotective properties, with higher concentrations on the face and . Sweat glands include eccrine types, which form spiral ducts opening directly onto the skin surface for through water and salt secretion, and types located in areas like the axillae and genitals. Collectively, skin appendages support essential physiological roles, such as insulation and sensory protection via , mechanical safeguarding of extremities by , lubrication and barrier enhancement through sebaceous secretions, and temperature regulation alongside immune defense via sweat glands. These structures also facilitate by providing reservoirs of epithelial cells for regeneration, particularly in split-thickness skin grafts where adnexal remnants enable epidermal regrowth. Their development and maintenance are influenced by hormonal and genetic factors, underscoring their role in both and adaptation to environmental stressors.

Overview

Definition

Skin appendages, also known as adnexa cutis, are specialized structures derived from the that form through invaginations or ingrowths of the primitive during embryonic development. These structures originate primarily from the surface , which gives rise to the and its associated derivatives, while interacting with the underlying to integrate into the skin's architecture. Characterized by their ectodermal epithelial components, skin appendages are embedded within the and extend variably into the , distinguishing them from the primary skin layers of the and . Unlike the continuous sheets of epidermal or dermal , appendages manifest as discrete, localized formations that arise at specific sites during embryogenesis, typically around the 8th to 12th weeks of . They contribute to overall skin by supporting protective, sensory, and regulatory functions, though they are not integral to the barrier-forming strata of the skin itself. Examples of skin appendages include hair follicles, nails, sebaceous glands, and sweat glands, each developing through patterned ectodermal thickenings that invaginate into the . This developmental process ensures their integration as autonomous units rather than extensions of the uniform epidermal layer.

Classification

Skin appendages are primarily classified into two broad categories based on their structure and origin: epithelial appendages and glandular appendages. Epithelial appendages, derived from the epidermal layer, include hair follicles and nails, which form through keratinization processes without secretory functions. Glandular appendages, also originating from the epidermis but specialized for secretion, encompass sebaceous glands and sweat glands, which produce sebum and sweat to maintain skin homeostasis. Within the glandular appendages, subtypes are distinguished by their secretory mechanisms. Sebaceous glands operate as glands, where entire cells disintegrate to release sebum, integrating with hair follicles in the pilosebaceous unit. In contrast, sweat glands are divided into (eccrine) glands, which secrete via without cell loss, and glands, which release secretions along with portions of the , primarily in specific body regions. Evolutionarily, skin appendages across vertebrates stem from a common placode-dermal cell unit in an ancient toothed , with variations like feathers in birds representing modified scale-like structures; in mammals, including humans, they have diversified into the epithelial and glandular forms described.

Hair Follicles

Anatomy

The is a complex, tubular structure that extends from the epidermal surface into the and , forming part of the pilosebaceous unit along with the and . It originates from the during embryological development and produces the shaft while anchoring it to the skin. The follicle is divided into three main segments: the infundibulum, isthmus, and inferior segment. The infundibulum extends from the epidermal surface to the duct opening, lined by continuous with the . The isthmus spans from the sebaceous duct to the bulge region, where the inserts, and features a keratinization pattern similar to the . The inferior segment, from the bulge to the follicle base, includes the hair bulb containing the dermal papilla, a mesenchymal structure critical for growth . The shaft, the visible portion emerging from the follicle, consists of three layers: the medulla (central core, often absent in fine hairs), the cortex (bulk of the shaft, providing strength and pigmentation via keratinized cells), and the (overlapping scale-like cells protecting the cortex). Within the follicle, the inner root sheath (IRS) surrounds the shaft, aiding in its shaping and anchorage, while the outer root sheath (ORS) extends continuously from the , serving as a reservoir for stem cells. The bulge region of the ORS, located at the arrector pili insertion, harbors multipotent stem cells essential for cyclic regeneration. Histologically, the matrix in the bulb exhibits high mitotic activity during the anagen phase, with matrix cells differentiating into the shaft and sheaths; the dermal papilla induces and maintains growth through signaling factors. Melanocytes in the bulb produce for color. Hair follicles receive a rich vascular supply from capillaries arising from the deep dermal vascular plexus, particularly surrounding the dermal papilla, which supports nutrient delivery and shows increased during the growth phase. Innervation includes sensory nerve fibers (Aδ and C fibers) for mechanosensation, , and detection, primarily in the mid-follicle and regions, as well as sympathetic fibers innervating the for piloerection in response to or stress. Quantitative aspects include an average follicle length of 3-5 mm on the , with the bulb approximately 0.1-0.2 mm; the human contains over 100,000 follicles, each capable of producing at a rate of about 1 cm per month during anagen.

Types and Distribution

Human hair is categorized into three primary types based on structure, pigmentation, and location: , vellus, and . Lanugo hair consists of fine, unpigmented strands that cover the fetal body during development and are typically shed before or shortly after birth. Vellus hair is short, fine, and lightly pigmented, forming the soft, downy covering on much of the body, such as the face and arms in adults. Terminal hair, in contrast, is coarser, thicker, and often pigmented, appearing prominently on the , eyebrows, eyelashes, and pubic regions. At birth, humans possess approximately 5 million hair follicles distributed across the body, with no new follicles forming postnatally. Density varies significantly by region; the exhibits the highest concentration, ranging from 100 to 150 follicles per square centimeter, while follicles are absent on the palms and soles. Other areas, such as the face and trunk, have lower densities, typically 50-100 follicles per square centimeter. influences distribution, particularly in androgen-sensitive areas like the face, where males develop denser growth, such as beards, due to higher testosterone levels during . Hair follicles undergo a cyclical process involving three main phases: anagen (active growth), catagen (transitional regression), and telogen (resting). On the , the anagen phase lasts 2-7 years, during which 85-90% of follicles are actively producing ; catagen follows for 2-3 weeks as the follicle shrinks; and telogen persists for about 3 months before shedding and renewal. Regional variations affect cycle duration; for instance, and follicles have abbreviated cycles, with anagen phases of only 1-4 months, resulting in shorter hair lengths compared to scalp hair.

Nails

Anatomy

The nail unit comprises several interconnected structures that form a protective plate on the dorsal aspect of the distal phalanges. The nail plate, the visible and rigid portion, is a translucent, convex structure composed primarily of compacted, hard derived from specialized epithelial cells. It overlies the nail bed, a soft, that adheres to the ventral surface of the plate via longitudinal ridges, providing support and attachment. The proximal nail fold, a skin-like extension, covers the nail root and includes the (cuticle) at its distal edge, while lateral nail folds enclose the sides of the plate. Distally, the forms a seal beneath the free edge of the nail plate, transitioning back to typical epidermal structure with a reappearing . Histologically, the nail matrix—the proliferative region at the nail root—lacks a granular layer, distinguishing it from the , and consists of dorsal and ventral components that contribute differentially to the plate's thickness and curvature. Onychocytes, the keratin-producing cells within the matrix, undergo cornification without forming keratohyalin granules or nuclear remnants, resulting in a highly organized, anuclear structure rich in and low in and water. The nail bed is thin, with a single layer of basal cells and no , featuring a dense network interspersed with glomus bodies for vascular regulation. Melanocytes are present in the matrix at approximately 217 per mm², contributing to pigmentation in the lunula, the pale distal portion of the visible matrix. Typical dimensions of the nail plate include a thickness of approximately 0.5 mm for fingernails and 1.5 mm for toenails (varying by sex, age, and digit), with fingernails averaging 0.5 mm (women) to 0.6 mm (men) and toenails 1.38 mm (women) to 1.65 mm (men) at the distal margin. Fingernails exhibit an average linear extension of 3 mm per month, while toenails advance at about 1 mm per month, reflecting inherent structural growth parameters. The nail unit receives its blood supply from branches of the radial and ulnar arteries, which form the superficial and deep palmar arches and subsequently give rise to proper digital arteries; these supply the proximal and lateral nail folds via a dorsal arcade approximately 0.5 cm proximal to the cuticle, while longitudinal subungual vessels nourish the and matrix through proximal and distal arcades. Innervation arises from paired digital nerves—dorsal branches for the proximal fold and palmar trifurcations for the and pulp—providing sensory functions including , touch, and detection across the unit.

Growth and Function

Nail growth occurs continuously from the nail matrix, a region of proliferating located beneath the proximal nail fold, producing the nail plate at an average rate of approximately 0.1 mm per day for fingernails. This process is influenced by hormonal factors, with elevated levels during accelerating growth by up to 10-20%. Minor trauma to the nail can also stimulate faster growth through mechanisms involving the lunula, the visible distal portion of the matrix, promoting keratinocyte proliferation. Full regeneration of a fingernail after complete loss typically takes 4-6 months, as the new plate emerges from the matrix and advances distally. Growth rate declines with age, slowing by about 0.5% per year starting around age 25 and becoming notably reduced after 50 due to decreased cellular turnover in the matrix. Nails serve essential physiological roles, providing counterpressure against the fingertip pulp to enhance tactile sensitivity and enable precise manipulation of small objects. They also protect the distal phalanges from mechanical injury and support fine motor tasks by stabilizing the fingertip during grasping. Growth variations include faster rates in the dominant hand, attributed to increased minor trauma from use, and seasonal differences, with during warmer months due to higher metabolic activity.

Glandular Appendages

Sebaceous Glands

Sebaceous glands are exocrine glands characterized by acinar structures composed of sebocytes that undergo differentiation and lipid accumulation before rupturing to release their contents. These glands are typically embedded in the mid-dermis and form part of the pilosebaceous unit, with their short ducts opening directly into the infundibulum of the , facilitating the delivery of sebum to the skin surface. In hairless regions such as the vermilion border of the and the of the nipples, sebaceous glands occur independently as ectopic or free glands, lacking association with follicles. Microscopically, the lipid-laden sebocytes give the gland a foamy appearance due to . The distribution of sebaceous glands covers virtually the entire except for the palms and soles, where hair follicles are absent. An adult contains approximately 2 to 3 million such glands, with the highest densities in seborrheic areas: up to 900 glands per cm² on the face and . Gland size and activity vary by region, being largest and most active on the , , and upper back. Sebaceous glands secrete sebum, a complex mixture comprising triglycerides, free fatty acids, wax esters, , , and cellular debris, which constitutes about 90% of the skin's surface . The secretion process is , with mature sebocytes lysing within roughly 1 week to expel contents; overall sebum production rate averages 1 to 2 mg/cm²/day on the . Sebum contributes to the skin's acid mantle, maintaining a surface of 4.5 to 5.5 through lipid-derived free fatty acids. Regulation of activity is primarily hormonal, with s such as testosterone and binding to nuclear receptors in sebocytes to stimulate proliferation, sebocyte differentiation, and via enzymes like . Activity peaks during due to surging levels during (typically ages 6 to 9 years) and continuing through , following an initial surge at birth; the total number of glands remains constant lifelong, but their size and output increase with hormonal influence.

Sweat Glands

Sweat glands are exocrine structures classified into two primary types: eccrine and glands. A third type, apoeccrine glands, arises from eccrine precursors during late childhood and is concentrated in the axillae and perineal areas, secreting copious watery sweat similar to eccrine glands but opening into follicles like apocrine ones. They become prominent post- and account for a substantial portion of axillary . Eccrine glands, also known as glands, produce a watery sweat primarily composed of and (NaCl), with concentrations typically ranging from 20–80 mmol/L Na⁺. These glands are distributed across nearly the entire body surface, numbering approximately 2–4 million in total, but are absent from the of the lips, external auditory canal, nail beds, , , and . In contrast, apocrine glands secrete a viscous, lipid-rich fluid containing proteins, sugars, and , which is initially odorless but can develop through bacterial decomposition on the skin surface. Apocrine glands become functionally active at and are confined to specific regions such as the axillae, perineal area (including , , and prepuce), areolae, nipples, face, , and perianal regions. Apocrine glands exhibit a more restricted distribution, with a ratio of approximately 1:1 relative to eccrine glands in the axillae and about 1:10 elsewhere on the body. Anatomically, eccrine glands consist of a coiled secretory portion located in the lower dermis or hypodermis, comprising clear cells, dark cells, and myoepithelial cells that facilitate secretion through a merocrine mechanism (exocytosis without loss of cellular material). Their duct is a straight, tubular structure lined with basal and luminal cells that ascends through the dermis and epidermis to open directly onto the skin surface via a pore. Apocrine glands are larger and positioned deeper in the dermis or subcutaneous tissue, featuring a branched secretory coil; their ducts empty into the upper portion of hair follicles rather than directly onto the skin surface, reflecting their close association with pilosebaceous units. Distribution of eccrine glands varies by body region, with the highest density on the palms and soles at approximately 250–700 glands per cm², decreasing to about 50–100 glands per cm² on the trunk and limbs. Modified forms of these glands include ceruminous glands, which are apocrine-derived and located in the external auditory canal to produce cerumen (earwax), and mammary glands in the breasts, which secrete . Eccrine glands can secrete up to 1–3 L of sweat per hour under maximal conditions, though typical rates are lower, with the fluid being hypotonic due to NaCl in the duct. secretion is generally scant and episodic, triggered by emotional or adrenergic stimuli rather than continuously, contributing to localized moisture in haired areas.

Functions

Protective and Sensory Roles

Skin appendages play crucial roles in protecting the body from environmental threats and facilitating sensory . Hair provides mechanical protection by acting as a physical barrier against abrasions and injuries to the underlying . Additionally, hair shields the from (UV) radiation, reducing the risk of damage from solar exposure. The arrector pili muscles enable piloerection, which traps air layers to enhance insulation and provide further mechanical defense. Nails serve as rigid structures that protect the from trauma and external impacts during daily activities. They also enhance grip and manipulation by countering pressure on the digit tips. Sebaceous glands secrete sebum, while sweat glands produce eccrine sweat; together, these form a hydrolipidic film on the skin surface that prevents by limiting . This film acts as a barrier against pathogens, with sebum-derived free fatty acids exhibiting properties to inhibit bacterial and fungal growth. In sensory functions, hair follicles are innervated by nerve endings that detect shaft deflection, contributing to tactile awareness. Merkel cells associated with hair follicles act as mechanosensory receptors, transducing gentle touch stimuli via adrenergic synapses to activate sensory neural pathways. In the nail unit, the nail bed and sterile matrix contain Meissner corpuscles and Merkel endings, which enable fine tactile discrimination and sensitivity to light touch. These receptors support precise sensory feedback essential for manual dexterity.

Thermoregulation and Excretion

Skin appendages play crucial roles in by facilitating heat dissipation and conservation, as well as contributing to minor of metabolic byproducts. Eccrine sweat glands, distributed across most of the body surface, are the primary effectors for evaporative cooling during thermal or exercise. These glands secrete a watery fluid that evaporates from the skin, dissipating heat equivalent to up to 2,430 J per gram of sweat evaporated, which can account for the majority of heat loss—often exceeding 80%—in hot, dry environments where metabolic heat production is high. In contrast, sweat glands, located in areas like the axillae and , contribute minimally to but activate during stress responses, producing a viscous triggered by emotional stimuli such as or anxiety via adrenergic innervation. Hair shafts enhance thermal insulation by trapping a layer of still air close to the skin, reducing conductive and convective heat loss, particularly in cooler conditions. This effect is amplified by piloerection, where arrector pili muscles contract to erect hairs, increasing the insulating air volume and minimizing radiative heat transfer; in primates and humans, this mechanism can reduce heat loss by altering the hair coat's effective thickness. Sebaceous glands support thermoregulation indirectly by secreting sebum, an oily mixture of triglycerides, wax esters, and squalene that forms a hydrophobic film on the skin and hair, preventing excessive evaporative water loss and maintaining barrier integrity during temperature fluctuations. Beyond temperature control, skin appendages aid in excretion, though their contribution is minor compared to renal and gastrointestinal routes. Eccrine sweat eliminates small amounts of (concentrations typically 20-25 mM, approximately 3-4 times plasma levels) and salts like sodium (20-80 mM), accounting for approximately 2-5% of the total renal solute load under normal conditions, with increased output during profuse sweating. Apocrine sweat and sebum provide negligible excretory roles, but sebum does transport minor , including and free fatty acids (comprising about 25% of its composition), which are byproducts of sebaceous cell breakdown. This excretory function helps clear without imposing significant physiological burden.

Embryological Development

Origin and Formation

Skin appendages originate from the surface of the , which differentiates into the and its derivatives under the inductive influence of the underlying beginning around the fifth week of gestation. This ectodermal layer, initially a single sheet of cells, thickens in response to mesenchymal signals to form the foundational structures for appendages such as , , and glands. The process involves reciprocal epithelial-mesenchymal interactions that pattern the skin and initiate appendage formation. Hair follicles develop from ectodermal placodes, localized thickenings of the , which first appear around the ninth week of . These placodes induce the formation of dermal condensates below them, leading to downward epithelial proliferation into the to form the hair bud by the twelfth week. This downward growth continues, establishing the hair bulb and papilla, with the first hairs emerging on the upper lip and scalp by this stage. Nail development begins with the appearance of the primary nail field on the dorsal aspect of the distal phalanges around the seventh to tenth week of , marked by ectodermal thickenings bordered by nail grooves. The nail matrix emerges from the proximal groove by the eleventh week, followed by the initial formation of the nail plate at week twelve. Keratinization of the nail plate commences around the fourteenth week, enabling progressive coverage of the nail bed. Glandular appendages arise from ectodermal buds associated with the or hair structures. Sebaceous glands form as lateral outgrowths from the upper portions of developing hair follicles starting in the thirteenth to fourteenth week of . Eccrine sweat glands originate as epidermal invaginations around the twelfth to thirteenth week, elongating into the to form coiled secretory portions by the twenty-fourth week, with initial appearance on palms and soles in the fourth month. Apocrine sweat glands develop later, emerging as outgrowths from hair follicle bulbs in specific regions like the axillae during the fifth month or later. The initiation and patterning of these appendages are governed by key molecular signaling pathways, including Wnt, BMP, and Shh. Wnt signaling promotes ectodermal commitment to epidermal fates and drives placode formation in hair and gland development. BMP acts to inhibit neural differentiation while spacing appendage sites by repressing placode formation in inter-follicular regions. Shh, expressed in epithelial buds, sustains proliferation and branching in structures like sweat glands and supports later stages of hair follicle morphogenesis. These pathways interact dynamically to ensure precise spatiotemporal control of appendage development.

Postnatal Development

Following birth, the fine, downy hairs covering much of the newborn's body are typically shed within the first few weeks, often by the end of the first month, to be replaced by vellus hairs that predominate during infancy and childhood. During this period, hair transitions from sparse vellus types to denser patterns, though most remains fine and unpigmented until . At , rising levels, particularly testosterone and its metabolite , drive the conversion of vellus hairs to thicker, pigmented terminal hairs in androgen-sensitive areas such as the , axillae, pubic region, and face in males. Nail growth rates in infancy are similar to those in young adults, approximately 3 mm per month for fingernails, before gradually slowing to peak again briefly in early and then declining steadily with age. By adulthood, toenail growth stabilizes at about 1 mm per month, but from age 25 onward, both fingernail and toenail growth rates decrease by roughly 0.5% annually, contributing to thicker, more brittle nails in later life. Apocrine sweat glands, present but inactive from birth, become functional at under the influence of sex hormones, secreting viscous, odorless fluid in areas like the axillae and that later break down to produce . Concurrently, sebaceous glands undergo during , enlarging and increasing sebum production in response to elevated androgens, which peaks in the third decade before stabilizing. Eccrine sweat glands, active since birth for , maintain output through young adulthood but show no significant postnatal . In aging, hair follicles in genetically susceptible individuals undergo progressive miniaturization, where terminal hairs revert to vellus-like structures, manifesting as androgenetic alopecia that affects approximately 80% of Caucasian men and 40% of women by age 70. This process shortens the anagen growth phase and is mediated by sensitivity in follicles. Sebaceous gland activity declines after age 60, reducing sebum output and contributing to drier skin, while eccrine sweat glands exhibit and diminished secretion, impairing and increasing risk. Hormonal fluctuations exert key influences on postnatal development; for instance, elevated during prolongs the anagen phase, accelerating growth and increasing nail growth rates by approximately 10% compared to non-pregnant states. Postpartum withdrawal often triggers temporary , with shedding resolving within months.

Clinical Significance

Disorders of Hair and Nails

Disorders of hair and nails encompass a range of pathologies affecting these epithelial appendages, often resulting from genetic, autoimmune, infectious, or inflammatory processes. Hair disorders primarily involve disruptions in follicle cycling, leading to excessive loss or growth, while nail disorders manifest as structural changes, infections, or inflammatory alterations. These conditions can significantly impact due to cosmetic concerns and associated pain, though most are manageable with targeted therapies.

Hair Disorders

Alopecia areata is an autoimmune condition characterized by patchy due to immune-mediated attack on follicles, disrupting the anagen phase of the normal growth cycle. It affects approximately 2.1% of the population, with a higher susceptibility in individuals with other autoimmune diseases. Androgenetic alopecia, the most common form of , is genetically determined and involves progressive miniaturization of follicles under the influence of s, leading to thinning primarily on the . By age 50, more than 50% of men and a substantial proportion of women experience this condition. refers to excessive terminal growth in women in a male-pattern distribution, typically caused by excess from ovarian or adrenal sources, such as in . It affects 5-10% of reproductive-age women and requires evaluation for underlying endocrine abnormalities.

Nail Disorders

Onychomycosis is a of the nail plate, most commonly caused by dermatophytes, leading to discoloration, thickening, and brittleness; the worldwide is approximately 5.5%, higher in adults and increasing with age due to factors like reduced peripheral circulation. Nail , an extension of psoriatic disease, often presents with pitting—small, pinhead-sized depressions in the nail plate resulting from parakeratotic shedding at the proximal matrix—along with and subungual . This affects up to 50% of patients and correlates with disease severity. is an inflammatory infection of the nail fold, usually acute and bacterial (e.g., or ), triggered by trauma or moisture exposure that breaches the protective barrier; chronic forms may involve Candida and irritants.

Congenital Disorders

Ectodermal dysplasias are a group of inherited disorders arising from defects in ectodermal tissue development, often featuring hypotrichosis (sparse or absent scalp and ) alongside abnormalities in , teeth, and sweat glands; the most common form, , results from mutations in genes like EDA. Nail-patella syndrome is an autosomal dominant condition caused by LMX1B gene mutations, characterized by nail dysplasia (triangular lunulae, ridging, or hypoplasia, worst in thumbnails), patellar hypoplasia, , and iliac horns; renal involvement occurs in about 30-50% of cases.

Diagnosis

Trichoscopy, or dermoscopic examination of the scalp and hair, is a non-invasive tool that reveals specific features like yellow dots in or perifollicular pigmentation in androgenetic alopecia, aiding in accurate diagnosis without biopsy in most cases. For nails, dermoscopy (onychoscopy) enhances visualization of subsurface structures, identifying fungal elements in (e.g., longitudinal spikes) or pitting patterns in , improving diagnostic precision over clinical inspection alone.

Disorders of Glands

Disorders of the sebaceous glands commonly manifest as acne vulgaris, a chronic inflammatory condition primarily affecting the pilosebaceous unit through the formation of comedones—non-inflammatory plugs of sebum and dead skin cells—and subsequent inflammatory lesions such as papules, pustules, and nodules. This disorder impacts more than 85% of teenagers, often resolving post-adolescence but persisting in some adults. Another benign proliferation is , characterized by enlarged sebaceous glands appearing as small, yellowish papules, predominantly in middle-aged or older adults, particularly on the face. Sweat gland disorders include primary , an idiopathic overactivity of eccrine sweat glands leading to excessive sweating beyond thermoregulatory needs, affecting approximately 3% of the population and commonly involving the palms, soles, and axillae. In contrast, anhidrosis represents a deficiency or absence of sweating, which impairs heat dissipation and elevates the risk of heat-related illnesses such as , especially in hot environments. Bromhidrosis arises from bacterial decomposition of apocrine sweat secretions, producing a pungent primarily from apocrine-rich areas like the axillae and . Tumors associated with sweat glands encompass , a benign adnexal derived from eccrine ducts, presenting as multiple small, firm papules typically on the eyelids and cheeks. involves chronic inflammation due to follicular occlusion and gland involvement, leading to recurrent painful nodules, abscesses, and sinus tracts in areas. Associated conditions include , which are ectopic sebaceous glands appearing as asymptomatic yellowish-white granules on the oral or genital mucosa. , or heat rash, results from occlusion of eccrine sweat ducts, causing retention of sweat and subsequent pruritic eruptions that vary by depth of blockage, from superficial clear vesicles to deeper inflammatory papules.

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