IA Cosmetology key terms

A 0-to-14 measure of how acidic or alkaline a water-based solution is, with 7 neutral. Hair, skin, and nails are mildly acidic, so products far from that range can swell the cuticle or irritate skin.

Destroying most harmful microorganisms on hard, nonporous implements and surfaces using an EPA-registered hospital-grade product mixed and timed per its label. It does not reliably kill bacterial spores, so it is not sterilization.

The complete destruction of all microbial life, including bacterial spores, usually by autoclave steam under pressure or dry heat. Required for items that may contact broken skin or blood, not for routine shears and combs.

A lower-level cleaning step that removes visible soil and reduces microorganism counts on tools, hands, and linens. It is done before disinfection and is not a substitute for it on implements that contact clients.

A virus or bacterium spread through contact with infected blood or body fluids, such as hepatitis B, hepatitis C, and HIV. Cosmetologists must follow standard precautions, including gloves and proper sharps disposal, when exposure is possible.

A manufacturer document listing a product's hazardous ingredients, safe handling, first-aid measures, and disposal instructions. Federal hazard communication rules require employers to keep these accessible to workers who use the products.

A small controlled application of a product, usually behind the ear or in the elbow crease, observed for 24 to 48 hours to detect allergic reaction before a full service. Required by many manufacturers for hair color and some adhesives.

The layered structure of skin: the epidermis (outer protective layer), the dermis (nerves, glands, vessels, collagen), and the subcutaneous layer (fat and insulation). Product penetration and treatment limits depend on which layer is reached.

The outermost layer of the epidermis, made of flattened dead keratinized cells that limit water loss and block most substances. Its condition determines how rough, dry, or absorbent skin appears.

A gland in the dermis that secretes sebum, an oily substance that lubricates skin and hair. Overactivity contributes to oily skin and comedones; underactivity contributes to dryness and flaking.

The repeating phases of a hair follicle: anagen (active growth), catagen (transition), and telogen (rest and shedding). Because follicles cycle independently, not all hair is growing at once, which affects waxing and laser timing.

The active growth stage of a hair follicle, lasting years on the scalp. Hair is most firmly anchored and most pigmented in this phase, which is why hair removal and chemical services behave differently here.

The resting stage of the hair growth cycle, ending with shedding of the club hair. Roughly 10 to 15 percent of scalp hairs are in telogen at any time, so normal daily shedding is expected.

The tough outer covering of a hair strand made of overlapping scale-like cells. When scales lie flat, hair looks shiny and resists chemicals; when they lift, hair feels rough and absorbs moisture or color faster.

The middle layer of a hair strand, containing keratin bundles and melanin pigment. It gives hair strength, elasticity, and color, and it is where chemical relaxers, color, and waving lotions do their work.

The ability of hair to absorb and hold moisture, determined by cuticle condition. Low porosity resists moisture and chemicals; high porosity absorbs quickly but loses moisture and color fast.

A wet-strand check in which a small section of hair is stretched to judge whether it returns to length or breaks. Good elasticity means the cortex is healthy enough for chemical services; poor elasticity signals damage.

A shampoo formulated near the natural acidity of hair and scalp, typically around pH 4.5 to 5.5. It helps close the cuticle after chemical services, improving shine and reducing color fade.

A permanent wave using ammonium thioglycolate at an alkaline pH, which swells the hair and breaks disulfide bonds quickly. It produces firm curl and is not used on hair already relaxed with sodium hydroxide.

A chemical product that straightens curly or wavy hair by breaking disulfide bonds in the cortex, usually with sodium hydroxide, lithium hydroxide, or guanidine. Timing and strand tests are critical to avoid breakage or burns.

A class of chemical compounds, including many oxidative hair dye intermediates, derived from coal tar or petroleum. They can cause allergic skin reactions, so patch tests and gloves are standard precautions.

A six-category classification of skin type based on pigmentation and how skin responds to ultraviolet light. Estheticians use it to predict sunburn risk and to guide laser, waxing, and peel decisions.

The pigment produced by melanocytes that gives skin, hair, and eyes their color and helps shield skin from ultraviolet radiation. Its amount and distribution determine Fitzpatrick type and affect treatment risk.

Darkening of skin caused by excess melanin, often after sun exposure, inflammation, or hormonal change. Treatments aim to fade it gradually, and aggressive peels or waxing over inflamed skin can worsen it.

Removing dead cells from the skin surface by mechanical scrubbing or chemical agents such as alpha hydroxy acids. It improves texture and product absorption but can cause irritation if overdone.

Describing an ingredient or product likely to clog pores and contribute to acne lesions. Estheticians choose noncomedogenic moisturizers and sunscreens for oily and acne-prone clients.

Removing comedones or milia with gentle pressure using fingertips or a properly disinfected extractor after softening the skin. It is limited to visible, superficial lesions and requires careful sanitation between clients.

A condition or circumstance that makes a service unsafe or inadvisable, such as active infection, recent surgery, or certain medications. Identifying these during consultation protects both client and practitioner.

Separation of the nail plate from the nail bed, leaving a whitish or hollow area, often caused by trauma, moisture, or aggressive filing. It is a contraindication for nail enhancements until the cause is resolved.

The visible hard covering of the fingertip or toe, made mainly of keratinized cells produced at the matrix. Its thickness, curvature, and condition determine how enhancements are applied.

The pink tissue beneath the nail plate, rich in blood vessels, to which the plate adheres. Damage to it can cause permanent distortion of the nail as it grows out.

The area at the base of the nail where new cells are produced and keratinized, forming the plate. Injury here affects the shape and thickness of all future nail growth.

The thin layer of dead tissue that seals the base of the nail plate against the skin, protecting the matrix from infection. It should be softened and gently pushed, never cut deeply.

A liquid applied to the natural nail plate before an enhancement to improve adhesion and reduce lifting, often by removing surface moisture or oils. Some are acid-based and require careful skin contact avoidance.

A temporary solvent applied to the natural nail to remove moisture and oils before primer and enhancement application. It evaporates quickly and helps the product bond without trapping residue.

The liquid component of acrylic nail systems, usually ethyl methacrylate, that polymerizes with powder polymer to form a hard enhancement. Proper ratio and ventilation protect both client and technician.

The powder component in acrylic nail systems that reacts with monomer liquid to form the hardened enhancement. Particle size and catalyst content affect set time and final strength.

A long-wearing coating cured under ultraviolet or LED light to harden, used over the natural nail. Proper removal by soaking avoids peeling that damages the nail plate surface.