NH Cosmetology key terms

A 0-to-14 scale measuring how acidic or alkaline a water-based solution is, with 7 neutral; hair and skin sit near the mildly acidic 4.5-to-5.5 range.

A shampoo formulated near the natural pH of hair and scalp, so it cleans without swelling the cuticle more than necessary and helps color-treated hair retain tone.

The thick middle layer of the hair shaft, made of elongated keratinized cells; it holds the pigment and moisture and gives hair its strength, elasticity, and curl pattern.

The outermost, overlapping scale layer of the hair shaft that protects inner structures; it must be lifted by alkaline products or heat before water, color, or relaxer chemicals can enter.

The innermost core of the hair shaft, often absent in fine or light-colored hair; it contributes little to strength and is not a target of salon chemical services.

The ability of hair to absorb and hold moisture, determined by cuticle condition; high porosity takes products quickly but loses moisture fast, while low porosity resists absorption.

The hair's ability to stretch when wet and return to its original length without breaking; poor elasticity signals damage and warns against strong chemical services.

The active growth stage of the hair cycle, lasting roughly two to seven years, during which the follicle produces a new hair shaft and scalp hair grows fastest.

The resting stage of the hair cycle, lasting about three months, when growth stops and the old hair is eventually shed as a new one begins forming below it.

The short transitional stage of the hair cycle, lasting a few weeks, when the follicle detaches from the blood supply and growth winds down before resting.

Partial or complete hair loss that may be hereditary, hormonal, stress-related, or caused by medical conditions or tight styling; a cosmetologist should refer clients rather than diagnose.

The diameter of an individual hair strand, described as fine, medium, or coarse; it affects how much product is needed and how quickly chemicals process.

The number of hairs per square inch on the scalp, described as thin, medium, or thick; it influences how much hair is available for cutting, sectioning, and styling.

The direction in which hair grows from the scalp, including the natural hairline, cowlicks, and whorls; it determines where tension, parting, and cutting lines should fall.

The angle at which hair is held away from the head while cutting, measured from the scalp; it controls the amount of layering and the resulting volume of the shape.

The first cut strand that sets the length, angle, and reference point for the rest of a haircut, ensuring both sides and all sections match consistently.

Dividing the head into controlled, even working areas with partings before cutting, coloring, or styling, so each subsection can be worked methodically and symmetrically.

A texturizing technique in which the shear tips cut into the ends of a section to soften a line, remove bulk, and create a blended, less solid finish.

A technique where shears are partially opened and slid along the hair strand to thin and blend length while softening weight, used mainly on longer shapes.

Using a brush and directional warm airflow to smooth the cuticle, create volume or bend, and set a finished shape; heat protection and control of tension are essential.

Shaping hair with heated tools such as flat irons, curling irons, and hot rollers; correct temperature selection and heat protectant reduce moisture loss and cuticle damage.

A hydrogen peroxide solution that opens the hair cuticle and supplies oxygen to develop color or lighten melanin; its strength is chosen by the desired lift and the hair's condition.

The natural pigment in the cortex that gives hair its color; eumelanin produces brown and black tones, while pheomelanin produces red and yellow undertones.

The warm color tones exposed when melanin is removed by lightening; failing to account for it is why a lifted result can appear brassy or orange instead of the target shade.

A dilute, typically semipermanent color applied after lightening to neutralize unwanted warmth or add a specific shade, restoring a controlled, even tone.

A small application of a color or chemical product on skin, usually 24 to 48 hours before service, to check for an allergic reaction before full application.

Processing a small sample of the client's hair with the intended chemical to predict timing, strength, and outcome before committing to the full service.

A strong alkaline cream, usually containing sodium hydroxide or a no-lye alternative, that straightens curl by breaking disulfide bonds in the cortex; it requires careful scalp protection.

A strong chemical link between sulfur atoms in adjacent keratin chains; it holds the hair's curl pattern and is broken by relaxers and perms, then reformed in the new shape.

A low-pH shampoo used after relaxing or perming to stop chemical action, remove residue, and rebuild disulfide bonds so the new shape holds safely.

A six-point classification of skin type based on how skin responds to sun exposure, used to judge burning risk and guide treatment intensity and sun protection advice.

Removing dead surface cells from the skin with a gentle scrub, enzyme, or acid product to smooth texture and brighten; it must be matched to skin sensitivity and recent treatments.

A condition or circumstance that makes a service unsafe or inadvisable, such as broken skin, infection, or recent surgery; identifying it protects both client and practitioner.

The visible hard keratin structure covering the nail bed; its condition, color, and surface reflect health and must be assessed before any nail enhancement service.

The pink tissue beneath the nail plate that supplies it with moisture and nutrients; damage or separation here can cause pain and should be referred to a physician.

The area at the base of the nail where new cells form and harden into the nail plate; injury to it permanently affects the shape and growth of the nail.

A fungal infection of the nail that may cause thickening, discoloration, and separation; it is contagious and requires medical treatment, so service should be refused.

Destroying most pathogenic organisms on nonporous tools and surfaces using an EPA-registered hospital-grade product, following the label's contact time and concentration.

The complete destruction of all microbial life, including spores, usually by autoclave or dry heat; used for items that may contact blood or broken skin.

The basic cleaning and lowering of microorganism counts on surfaces and linens through washing and routine housekeeping; it is the first step before disinfection.

A document supplied with a chemical product that lists its hazards, safe handling, first-aid measures, and storage requirements; it must be kept accessible in the salon.