Anatomy & Sciences
Anatomy and basic sciences form the largest single block of the California written exam, roughly 22% of all questions. This chapter covers the skin, hair, nails, microorganisms, and the bones, muscles, and nerves that licensees touch during every service.
The Skin: A Three-Layer Organ
Skin is the largest organ of the human body and has three main layers. From the outside in they are the epidermis, the dermis, and the subcutaneous (subcutis) layer. The epidermis is what licensees can legally touch with topical products; deeper layers belong to the practice of medicine.
The Five Layers of the Epidermis
From deepest to most superficial, the epidermis has the stratum basale (the basal cell layer where new cells are born), the stratum spinosum (spiny layer), the stratum granulosum (granular layer), the stratum lucidum (a clear layer found only on palms and soles), and the stratum corneum (the dead, keratinized outer layer that you exfoliate and cleanse).
Melanocytes and Skin Color
Melanocytes are specialized cells in the stratum basale that produce melanin, the pigment that gives skin its color and helps shield deeper cells from ultraviolet light. The number of melanocytes is similar across all people; the difference in skin tone comes from how much melanin each cell produces and how it is distributed.
The Dermis and Subcutaneous Layer
The dermis lies under the epidermis and contains collagen, elastin, blood vessels, nerves, sweat glands, sebaceous (oil) glands, and hair follicles. The subcutaneous layer is mostly fat and connective tissue that cushions and insulates the body. Most professional skin services aim to improve the appearance of the epidermis without injuring these deeper layers.
Hair Structure and the Follicle
A hair shaft has three concentric layers: the medulla (innermost core, sometimes absent in fine hair), the cortex (middle layer that holds pigment and gives hair its strength and elasticity), and the cuticle (outer protective scales). The hair grows from the follicle, which is fed by the dermal papilla and surrounded by the bulb at its base.
Phases of Hair Growth
Each hair cycles through three phases. Anagen is the active growing phase that can last 2–7 years on the scalp. Catagen is a short transition phase of about 1–2 weeks. Telogen is the resting/shedding phase that lasts roughly 3 months before the follicle re-enters anagen. About 85–90% of scalp hairs are in anagen at any moment.
Nail Anatomy
The nail plate is the hard keratin you polish. It grows from the matrix, the only living part of the nail unit, hidden under the proximal nail fold. The lunula is the visible white half-moon at the base, which is the front edge of the matrix. The free edge is the part that extends beyond the fingertip. The eponychium is the skin fold at the base; the cuticle is the thin layer of dead tissue that clings to the plate; the hyponychium is the seal of skin under the free edge.
Bacteria: Cocci, Bacilli, and Spirilla
Bacteria are one-celled microorganisms classified by shape. Cocci are round and include staphylococci (cluster-forming, can cause boils and impetigo) and streptococci (chain-forming, can cause strep throat and skin infections). Bacilli are rod-shaped and include the agents of tuberculosis and tetanus. Spirilla are spiral-shaped and include the bacteria that cause syphilis and Lyme disease. Most bacteria are non-pathogenic; only a minority cause disease.
Viruses, Fungi, and Parasites
Viruses are non-living particles that hijack host cells; common salon concerns include hepatitis B and C, HIV, human papillomavirus (warts), and herpes simplex. Fungi include the yeasts and molds that cause ringworm and athlete's foot. Parasites such as head lice (Pediculus capitis) and the itch mite (scabies) feed on the host. All can spread through shared implements, towels, or skin-to-skin contact, which is why single-use items are discarded and multi-use items are disinfected.
Common Skin and Scalp Disorders
Acne is a chronic disorder of the pilosebaceous unit; estheticians can perform extractions on non-inflamed comedones but cannot treat cystic acne medically. Rosacea, eczema, and psoriasis are medical conditions; licensees can adapt service (gentle products, avoid irritation) but cannot diagnose or prescribe. Dandruff (pityriasis) is a scalp condition; alopecia areata and androgenetic alopecia involve hair loss and warrant a physician referral; tinea capitis (scalp ringworm) is a contagious fungal infection requiring medical care and refusal of service.
Common Nail Disorders
Onychomycosis is a fungal infection of the nail plate and bed and is contagious; service should be declined and the client referred. Onycholysis is the separation of the nail plate from the bed and can result from trauma, allergy, or disease; do not apply enhancements over a separated plate. Paronychia is an infection of the surrounding tissue (often bacterial) presenting as redness, swelling, and sometimes pus; refuse service and refer. An ingrown nail (onychocryptosis) is the lateral edge of the plate growing into the surrounding skin; gentle filing of the free edge is appropriate, surgical removal is not.
Bones, Muscles, and Nerves of the Head, Neck, and Hands
Key skull bones include the frontal, parietal, occipital, and temporal; the mandible (lower jaw) and maxillae (upper jaw) shape the face. The major facial muscles include the frontalis (raises brows), orbicularis oculi (closes eye), orbicularis oris (closes mouth), masseter (chews), and the platysma (broad neck muscle). Cranial nerve VII (facial nerve) controls facial expression; cranial nerve V (trigeminal) carries facial sensation. In the arm and hand, the radial, median, and ulnar nerves supply movement and sensation, and the flexor and extensor muscles move the wrist and fingers. Basic knowledge supports safe, comfortable massage during shampooing, facials, and manicures.