IA Cosmetology cheat sheet

The three main layers of the hair shaft are the cuticle (outer protective layer), cortex (middle layer containing melanin and keratin), and medulla (innermost layer, often absent in fine hair).

The pH scale runs 0–14; hair and skin are naturally acidic at pH 4.5–5.5. The isoelectric point of hair is pH 4.5–5.5, where the fiber is strongest and least swollen.

Disulfide bonds are broken by reducing agents (thioglycolate, pH 9–10) and re-formed by oxidizing agents (hydrogen peroxide, sodium bromate) during permanent waving and relaxing.

The hair growth cycle: anagen (active growth, 2–7 years), catagen (transition, 2–3 weeks), telogen (resting, 3 months), and exogen (shedding).

The rule of thumb for developer volume: 10 vol = 3% H2O2, 20 vol = 6%, 30 vol = 9%, 40 vol = 12%. Each 20 vol lifts approximately one to two levels.

The three types of side bonds in hair are hydrogen bonds (broken by water, heat), salt bonds (broken by pH change), and disulfide bonds (broken by chemicals); hydrogen and salt bonds account for about two-thirds of hair's strength.

Bacteria are prokaryotic and reproduce by binary fission; viruses are obligate intracellular parasites and are not killed by standard disinfectants at the same rate. Fungi include molds and yeasts and are controlled by fungicidal agents.

Infectious agents are categorized by resistance: bacterial spores > mycobacteria > fungi > viruses > vegetative bacteria. Sterilization destroys all microbial life including spores; disinfection destroys pathogens on surfaces.

The two levels of decontamination are cleaning (removing debris) and disinfection (killing pathogens). Hospital-grade disinfectants must be EPA-registered and used at the label's contact time.

Hair texture (fine, medium, thick) refers to the diameter of a single strand; density refers to the number of hairs per square inch; porosity refers to the hair's ability to absorb moisture.

Low-porosity hair has a tightly closed cuticle and resists moisture; high-porosity hair has a raised cuticle and absorbs and loses moisture quickly. Porosity is tested by the float test or by observing how quickly hair absorbs water.

The hair elasticity test: wet a strand and stretch it; healthy hair stretches 50% of its length and returns. Less than 50% indicates weak hair; no return indicates breakage risk.

Permanent wave processing time depends on hair porosity, temperature, and the strength of the reducing agent. Do not process hair that has been treated with a relaxer or a thio-based product without a patch test.

Curl diameter in a perm is determined by the rod size: smaller rods produce tighter curls, larger rods produce looser waves. The base placement (on-base, half-base, off-base) controls volume.

The two types of hair lighteners are oil lighteners (no lift beyond one level, gentle) and cream lighteners (up to seven levels of lift, used with developer).

Thermal styling safety: the curling iron barrel should be tested on a tissue paper; if the paper scorches, the iron is too hot. Use a heat protectant and avoid holding the iron on one section for more than a few seconds.

Shampoo selection is based on hair condition: clarifying shampoos remove product buildup; moisturizing shampoos contain humectants; medicated shampoos contain active ingredients such as ketoconazole or salicylic acid.

The three types of hair relaxing are lye (sodium hydroxide, pH 12–14), no-lye (calcium hydroxide plus guanidine, pH 9–10), and thio (ammonium thioglycolate, pH 9–10). Lye relaxers require a base cream.

The layers of the epidermis from deepest to surface: stratum germinativum (basale), stratum spinosum, stratum granulosum, stratum lucidum (only on palms and soles), and stratum corneum.

The skin barrier is the stratum corneum; it is composed of corneocytes and intercellular lipids (ceramides, cholesterol, fatty acids) in a brick-and-mortar arrangement.

Skin types: normal, dry (alipidic), oily (lipid), combination, and sensitive. Skin conditions include dehydration, acne, rosacea, and hyperpigmentation.

Fitzpatrick skin phototypes I–VI classify sun reactivity: type I always burns and never tans; type VI never burns and deeply tans. Higher types have a greater risk of post-inflammatory hyperpigmentation.

The ABCDE rule for melanoma: Asymmetry, Border irregularity, Color variation, Diameter greater than 6 mm, and Evolving (changing) lesion.

Common facial treatments include cleansing, exfoliation (mechanical or chemical), extraction, massage, mask, and moisturizer. Chemical exfoliants include alpha hydroxy acids (AHAs, water-soluble) and beta hydroxy acids (BHAs, oil-soluble, e.g., salicylic acid).

Contraindications for facial treatments include active infection, recent surgery, sunburn, open lesions, and use of isotretinoin (Accutane) within the past six months.

The three main skin cancer types are basal cell carcinoma (most common, pearly nodule), squamous cell carcinoma (scaly patch), and melanoma (most dangerous, asymmetric mole).

Product ingredients: humectants (glycerin, hyaluronic acid) attract water; emollients (oils, fatty alcohols) soften and smooth; occlusives (petrolatum, dimethicone) prevent water loss.

Nail anatomy: the nail plate (visible nail), nail bed (skin under the plate), matrix (produces new cells), cuticle (dead tissue at the base), eponychium (living skin at the base), hyponychium (skin under the free edge), and lunula (whitish half-moon at the base).

The nail plate is composed mainly of keratin; it has no nerves or blood vessels. The nail grows approximately 0.1 mm per day (about 3 mm per month); toenails grow slower (about 1 mm per month).

Nail diseases vs. disorders: onychomycosis (fungal infection) and paronychia (bacterial infection) are diseases requiring medical referral; onychorrhexis (split nails) and leukonychia (white spots) are disorders.

The three types of nail tips are full-well, half-well, and no-well (also called French or natural). Tip size is chosen by matching the width of the natural nail's free edge.

Acrylic (liquid-and-powder) systems use a monomer liquid (ethyl methacrylate, EMA) and a polymer powder. The ratio of liquid to powder controls the strength and curing time; a dry bead is too much powder, a wet bead is too much liquid.

Gel nails cure under UV or LED light; the photoinitiator in the gel absorbs light and causes polymerization. LED cures faster than UV for most gels.

Nail preparation: sanitize hands, remove old product, file the free edge, gently push back the cuticle, and remove shine from the nail plate with a buffer. Do not over-file the nail plate, which can cause thinning and infection.

Disinfection of implements: remove debris, wash with soap and water, then immerse in an EPA-registered hospital-grade disinfectant for the label's contact time (often 10 minutes). Porous items (wooden sticks, emery boards) cannot be disinfected and must be discarded.

Nail product removal: acetone dissolves acrylics and gels; wraps with acetone-soaked cotton and foil are used for gel polish. Never use a drill on the natural nail plate at high speed without proper technique.