7.2 Functions of the Skin, Glands & the Acid Mantle

Functions of the Skin, Glands and the Acid Mantle

Ohio State Board Exam Alert: The Board's blueprint lists "Functions of the Skin" as its own leaf, separate from skin structure and skin diseases. Function questions are about what the skin does — and about the two glands whose behaviour explains almost everything a nail technician observes on hands and feet.

Structure explains what the skin is made of; function explains why the rules of practice are what they are. Every infection-control rule in Chapter 4713-15 exists because the skin's protective function has limits, and every break in it is a breach of the body's first line of defence.

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1. The Six Primary Functions of the Skin (SHAPES)

The physiological functions of the skin are easily memorized using the standardized acronym SHAPES:

┌────────────────────────────────────────────────────────────────────────┐
│                     THE SIX FUNCTIONS OF THE SKIN                      │
├────────────────────────────────────────────────────────────────────────┤
│ S ──► SENSATION: Detects touch, pressure, temperature, and pain.       │
│ H ──► HEAT REGULATION: Vasodilation/sweating vs vasoconstriction.      │
│ A ──► ABSORPTION: Transdermal uptake of lipids, vitamins, and oils.    │
│ P ──► PROTECTION: Acid mantle, stratum corneum, and melanin barrier.   │
│ E ──► EXCRETION: Sudoriferous sweating expels water, salts, and urea.  │
│ S ──► SECRETION: Sebaceous sebum lubricates and creates acid mantle.   │
└────────────────────────────────────────────────────────────────────────┘

1. Sensation

Millions of microscopic sensory nerve endings distributed throughout the skin transmit tactile data directly to the brain and spinal cord:

• Meissner's Corpuscles: Located in the superficial papillary dermis; detect light touch, delicate fluttering, and low-frequency vibrations.
• Pacinian Corpuscles: Located deep in the reticular dermis and subcutaneous tissue; detect firm pressure and high-frequency vibrations.
• Merkel Discs: Located in the basal epidermis; detect sustained light pressure and texture discrimination.
• Free Nerve Endings: Located throughout the epidermis and dermis; detect pain, temperature (heat and cold), and mechanical itch.

2. Heat Regulation (Thermoregulation)

The skin maintains internal core body temperature at approximately 98.6°F (37°C) through vascular and glandular feedback:

• Cooling Mechanisms (Hyperthermia Response): When the body overheats, dermal capillaries dilate (vasodilation), shunting warm blood to the surface so heat radiates outward into the environment. Simultaneously, sudoriferous (eccrine) glands secrete sweat across the epidermis; evaporation of this water removes latent heat, cooling the cutaneous surface.
• Warming Mechanisms (Hypothermia Response): When exposed to cold, dermal capillaries narrow (vasoconstriction), shunting blood away from the skin and extremities inward to core organs. Simultaneously, tiny arrector pili muscles contract, pulling hair follicles upright (producing goosebumps) to create an insulating air layer.

3. Absorption

Although the stratum corneum is designed to prevent water and microbes from entering, it selectively absorbs certain lipid-soluble compounds:

• Lipid-Soluble Penetration: Fat-soluble vitamins (A, D, E, and K), essential fatty acids, and small-molecule botanical oils (such as jojoba and squalane) penetrate intercellular lipid lamellae.
• Salon Application: Nourishing massage oils and intensive lotions applied during manicures and pedicures penetrate superficial epidermal layers, restoring flexibility and hydration.
• Chemical Toxicity Warning: Hazardous chemicals—such as pure acetone, monomer liquids, or toxic solvents—can also be absorbed through the skin, emphasizing why technicians must wear chemical-resistant nitrile gloves.

4. Protection

The skin serves as an impervious tripartite biological defense shield:

• Mechanical & Physical Barrier: The dense keratin corneocytes of the stratum corneum resist abrasion, impact, and puncture, while subcutaneous fat cushions underlying bones.
• Chemical & Microbial Barrier: The acid mantle (surface hydrolipid film with a pH of 4.5 to 5.5) suppresses pathogenic bacteria, fungi, and parasites.
• Photoprotective Barrier: Basal melanocytes produce melanin pigment, which forms protective supranuclear caps over keratinocyte DNA, absorbing mutagenic ultraviolet (UV) radiation.

5. Excretion

Sudoriferous (sweat) glands excrete perspiration across the skin surface. Sweat is composed of 99% water, sodium chloride, potassium, lactic acid, and minute quantities of metabolic cellular waste products, including urea and ammonia.

6. Secretion

Sebaceous (oil) glands secrete sebum, a lipid-rich substance containing triglycerides, squalene, and cholesterol. Sebum lubricates and softens the epidermal stratum corneum, waterproofs the hair shaft, prevents excessive moisture evaporation, and blends with sweat to create the acid mantle.

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2. Cutaneous Glands, Secretions & The Acid Mantle

Sudoriferous Glands (Sweat Glands)

Sudoriferous glands are coiled tubular glands situated in the dermis and hypodermis that excrete sweat to assist in thermoregulation and waste excretion:

• Eccrine Glands: Distributed over the entire body, but extraordinarily dense on the palms of the hands and soles of the feet. Eccrine glands secrete clear, watery, odorless perspiration (99% water, plus sodium chloride, vitamin C, and traces of urea) directly onto the epidermal surface through sweat pores to cool the body.
• Apocrine Glands: Located in the axillary (underarm) and genital regions, opening into hair follicles. They secrete a thicker sweat containing fatty acids and proteins; bacterial breakdown of these secretions produces body odor. Active primarily during emotional stress and puberty.

Sebaceous Glands (Oil Glands)

• Structure & Secretion: Sac-like alveolar glands located in the dermis, almost always connected to hair follicles. They secrete sebum, an oily lipid mixture that lubricates and waterproofs the stratum corneum and hair shaft.
• CRITICAL EXAM FACT — ABSENCE ON PALMS AND SOLES: Sebaceous glands are present across the entire body EXCEPT on the palms of the hands and soles of the feet!

  Clinical Significance: Because the palms and soles contain zero sebaceous glands, they produce no natural sebum to lubricate the stratum corneum. Consequently, the hands and feet dry out rapidly, crack, and form calluses far more readily than other body areas. This biological reality is why rich emollient creams, heavy foot butters, and warm paraffin wax treatments are clinically essential in professional manicures and pedicures.

The Acid Mantle: The Skin's Chemical Shield

• Formation: On the epidermal surface, oily sebum mixes with acidic perspiration and intercellular lipids to form a microscopic hydrolipid film known as the acid mantle.
• Optimal pH Range: The healthy acid mantle maintains a mildly acidic pH range of 4.5 to 5.5.
• Biological Function: The acidic environment acts as a natural germicide, inhibiting the colonization and proliferation of alkaline-loving pathogenic bacteria (Staphylococcus, Streptococcus) and fungi. It also helps neutralize alkaline chemicals that touch the skin.
• Salon Hazard — Stripping the Acid Mantle: Frequent handwashing with harsh alkaline bar soaps, constant immersion in pure acetone, or exposure to monomer liquids strips away the acid mantle and dissolves intercellular lipids. This induces irritant contact dermatitis—characterized by erythema, pruritus (itching), painful fissures, and heightened susceptibility to bacterial infection. Nail technicians must wear chemical-resistant nitrile gloves and regularly apply pH-balanced moisturizing lotions.

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3. Master Histology & Physiology Summary Table

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4. Clinical Scenarios & State Board Exam Traps

Scenario 1: Severe Dry, Cracked Heels

A pedicure client presents with thick, yellowed calluses on her heels containing deep, painful fissures that sting when walking. She wonders why her heels are so dry while the rest of her skin is naturally oily.

• Clinical Explanation: The soles of the feet contain zero sebaceous (oil) glands and are subjected to continuous mechanical weight and friction. Without natural sebum to lubricate the stratum corneum, the skin thickens into calluses and cracks.
• Professional Treatment: Soften the calluses with a professional callus-softening lotion, gently smooth the dead stratum corneum using a sanitized abrasive foot file (never a Credo blade!), and apply an intensive urea- or ceramide-based foot cream followed by a warm paraffin treatment.

Scenario 2: Contact Dermatitis in a Nail Technician

A technician who rarely wears gloves when performing monomer and polymer acrylic services develops dry, red, scaling, and intensely itchy skin between her thumb and index finger.

• Clinical Explanation: Repeated skin contact with volatile acrylic monomers and pure acetone stripped the skin's lipid barrier and destroyed the acid mantle (pH 4.5–5.5), causing occupational contact dermatitis.
• Preventive Protocol: The technician must wear chemical-resistant nitrile gloves for all chemical procedures, avoid skin contact with uncured monomers, wash hands with mild pH-balanced liquid soap, and apply barrier repair lotions.

Master State Board Traps to Avoid

• Trap 1: Believing the epidermis has blood vessels. The epidermis is strictly avascular. Any manicuring action that draws blood has punctured into the vascular dermis.
• Trap 2: Believing the stratum lucidum is present everywhere. The stratum lucidum is found ONLY on the palms of the hands and soles of the feet.
• Trap 3: Believing palms and soles produce natural oil. Palms and soles contain NO sebaceous glands; they contain only eccrine sweat glands.
• Trap 4: Confusing Meissner's and Pacinian corpuscles. Meissner's corpuscles reside in the superficial papillary dermis and detect light touch; Pacinian corpuscles reside deep in the reticular dermis/hypodermis and detect deep pressure.