Skin Theory: Behavior and Medical Factors

Vocabulary practice flashcards covering skin behavior, six primary skin functions, receptor types, cell renewal, wound healing phases, absorption pathways, and medical contraindications.

Somatosensory System

A network of nerve endings and touch receptors that detect sensations—such as hot, cold, rough, pressure, itch, and pain—and send signals to the nervous system and the brain.

Mechanoreceptors

Sensory receptors responsible for sensing sensations of pressure, vibrations, movement, and texture; includes Merkel cells, Meissner's corpuscles, Ruffini endings, and Pacinian corpuscles.

Merkel Cells

Sensory cells located in the basal layer of the epidermis that are responsible for detecting pressure and vibration.

Meissner's Corpuscles

Sensory receptors located in the upper dermis that project into the epidermis to perceive light touch and texture; found in the palms, lips, tongue, feet, eyelids, fingertips, and face.

Ruffini's and Pacinian Corpuscles

Sensory receptors located in the dermis and along joints, tendons, and muscles that sense skin stretching, vibration, and limb movement.

Thermoreceptors

Sensory nerve structures responsible for sensing hot and cold temperatures; includes Krause end bulbs and free nerve endings.

Krause End Bulb

Cold-sensing thermoreceptors found in the eyes, lips, tongue, connective tissue, and genitals.

Nociceptors (Pain Receptors)

Over 3 million sensory receptors distributed across the skin, muscles, bones, blood vessels, and some organs that detect pain; derived from the Latin root 'noci-' meaning 'injurious' or 'hurt'.

Proprioceptors

Over 3 million sensory receptors located in tendons, muscles, and joints responsible for sensing different body parts positioned in relation to each other and the environment (from the Latin 'proprius' meaning 'one's own').

Vasodilation

The widening of blood vessels when the body gets warm to allow heat to evaporate; utilized in esthetics via steamers, hot towels, electric masks, and high frequency to increase microcirculation.

Vasoconstriction

The narrowing of blood vessels when the body is cold to keep heat near essential organs; utilized in esthetics via cool towels, jade rollers, cool masks, and cold globes to reduce redness and slow inflammation.

Thermogenesis

The process of small muscular movements (shivering) triggered when core body temperature drops in order to expend energy and generate heat.

Transdermal Penetration

The process by which molecules and essential substances pass through the skin and penetrate via the epidermis into the deeper tissues or bloodstream.

Intercellular Space Absorption

A pathway of transdermal absorption where lipid-soluble products travel through the microscopic spaces between corneocytes.

Transcellular Diffusion

A primary transdermal absorption route where molecules pass directly through the interior of the corneocytes.

Occlusion

The application of a substance or barrier (such as a specialized plastic mask) to the skin that air cannot penetrate, used to enhance product penetration.

Corneotherapy

A specialized area of study focused on maintaining and improving the health, structure, and function of the skin's permeability barrier.

Acid Mantle

The first line of defense in the skin's barrier with a healthy pH range of 4.5-5.5; composed of sebum mixed with natural moisturizing factors (NMF) to inhibit harmful bacteria, prevent inflammation, and limit transepidermal water loss (TEWL).

Stratum Corneum

The outermost epidermal layer, approximately 15-20 cell layers thick, containing dead, flattened squamous cells (corneocytes) that lack a nucleus or organelles.

Desmosomes

Filamentous protein attachments that bind corneocytes together for structural support, beginning in the spiny layer and serving as targets for chemical exfoliation modalities like alpha hydroxy acids (AHAs).

Keratinization

The chemical conversion of living epidermal cells into dead protein cells (also known as cell renewal), which generally takes 4 to 6 weeks.

Soft Keratin

The flexible type of keratin protein produced by the skin, in contrast to the hard keratin produced in hair and nails.

Desquamation

The natural, continuous shedding, peeling, or coming off in scales of the stratum corneum (horny layer) of the epidermis.

Mechanical Exfoliation

The process of using an abrasive material or physical device (such as scrubs, clays, gommage, microdermabrasion, or ultrasonic spatulas) to stimulate the removal of the upper layer of the stratum corneum.

Chemical Exfoliation

The process of using natural substances such as enzymes, alpha hydroxy acids (AHAs), or beta hydroxy acids (BHAs) to dissolve the intercellular bonds holding dead skin cells together.

Hemostasis

The immediate first phase of wound healing (Day 1) that activates blood-clotting factors to halt blood loss; absent in superficial wounds that do not penetrate the circulatory system.

Proliferation

The third phase of wound healing starting 2 days after injury and lasting up to 3 weeks, characterized by epithelialization (cell renewal), collagen synthesis, and extracellular matrix (ECM) reorganization.

Maturation (Remodeling)

The fourth phase of wound healing spanning from the 3rd week to 1 year, where extracellular matrix remodeling continues, the wound contracts and gains strength, and post-inflammatory hyperpigmentation may emerge.

Post-Inflammatory Hyperpigmentation (PIH)

Excess production of melanin that results in darker patches of skin color following an inflammatory response or injury.

Melanocytes

Immune and pigment cells located in the basal layer of the epidermis that synthesize melanin and distribute melanosomes to keratinocytes.

Melanosomes

Packets of melanin pigment produced within melanocytes and distributed to approximately 38 surrounding keratinocytes.

Tyrosinase

The enzyme that triggers the chemical production of melanosomes within melanocytes during melanogenesis.

Langerhans Cells

Immune cells originating in bone marrow and primarily located in the stratum spinosum (comprising 2%-5% of epidermal cells) that recognize, capture, and destroy invading antigens before routing them to the lymphatic system.

Melanogenesis

A multi-stage chemical process triggered by UV radiation, heat, friction, stress, or trauma in which tyrosine is converted into dopa to synthesize melanin.

Eccrine Sweat Gland

A major sudoriferous gland stimulated by the sympathetic nervous system that secretes water and salt (NaCl) directly onto the skin surface to aid in thermoregulation and excretion.

Apocrine Sweat Gland

A sweat gland located in the underarms, genitals, breasts, and eyelids that remains inactive until stimulated by hormones during puberty; triggered by adrenaline and responsible for body odor.

Sebum

A complex mixture of non-polar lipids—including triglycerides, wax esters, 10%-20% squalene, and cholesterol—secreted by sebaceous glands to keep the skin lubricated, water-resistant, and protected.

Meibomian Cyst

A non-extractable cystic nodule along the lash line caused by the blockage of the meibomian duct by dead cells, which prevents the proper secretion of meibum oil over the tear film.

7-Dehydrocholesterol (7-DHC)

A fatty acid precursor located in the basal and spinosum layers of the epidermis that converts into vitamin D3 upon exposure to UVB rays.

Calcitriol

The active hormone form of vitamin D ($1,25\text{-}(\text{OH})_2\text{ vitamin D}$) processed by the liver and kidneys whose primary function is to regulate calcium and phosphate levels in the body.