HI Cosmetology cheat sheet

Growth patterns: hair grows in three basic patterns - straight, wavy (cowlick), and circular - plus a whorl at the crown; cutting against a circular pattern causes gaps, so reduce length gradually and blend with the natural flow.

Angle-to-elevation rule: 0° = blunt/one-length at the perimeter; 45° = graduated or wedge; 90° = uniform layers; 180° = long layers/shag. Elevation controls where weight builds.

Guide types: a stationary guide keeps all lengths equal to the first section; a traveling guide moves with each new section and follows the previous cut; a combination guide uses both within one haircut.

Tapering vs. fading: a taper leaves visible weight/ridge at the neckline or sideburn; a fade removes weight gradually to skin (skin fade = zero blade or razor). Clipper-over-comb removes bulk; shear-over-comb blends.

Beard and mustache design: outline is set by the client's natural growth and facial structure; a shaving beard line follows the jawline or is raised/rounded; mustache is leveled at the top lip; sideburn points are squared, rounded, or tapered to match the cut.

Straight-razor safety: hold with the blade edge away from skin when not shaving; stretch skin taut at 30–45°; shave with the grain first, then across; never shave over a raised mole, wart, or broken skin.

Sanitation hierarchy: clean = soap and water; disinfect = EPA-registered hospital-grade tuberculocidal product on nonporous implements; sterilize = autoclave or dry heat for porous/absorbent items. Blood spill: stop, gloves, disinfect with an EPA-registered tuberculocidal product per label contact time.

Tool rules: shear blades are disinfected after each client (never immersed in quats if the manufacturer forbids it); clipper blades are disinfected and oiled; neck strips and capes are single-use or laundered between clients.

Permanent wave and relaxer timing on barbered hair: a sodium hydroxide relaxer must never contact hair previously treated with a thio-based relaxer without a strand test; ammonium thioglycolate (perm) and hydroxide relaxers are incompatible in the same service.

pH scale: 0–14; 7 is neutral; hair and skin sit near pH 4.5–5.5. The hair shaft swells in alkaline solutions and contracts in acidic ones; acid-balanced shampoos close the cuticle.

Hair structure: cuticle (protective, 6–10 overlapping layers), cortex (80–90% of the fiber; holds melanin, disulfide bonds, and moisture), medulla (innermost, may be absent in fine hair).

Bonds: disulfide bonds give strength and shape and are broken by relaxers and perms; hydrogen bonds are broken by water and reform on drying (wet-set); salt bonds break with pH change; peptide bonds are broken only by strong chemicals (damage).

Permanent wave chemistry: ammonium thioglycolate (pH 8.5–9.5) reduces disulfide bonds; the thio relaxer is the same chemistry with higher concentration; neutralizer (hydrogen peroxide or sodium bromate) rebuilds bonds. Glyceryl monothioglycolate (GMTG) is an acid perm (pH 6.5–7) and needs heat.

Hydroxide relaxers: sodium, potassium, lithium, and guanidine hydroxide (no-lye) are lye-based, pH 12–14, and cause lanthionization (permanent conversion of disulfide to lanthionine). They cannot be neutralized back; hair is permanently straightened.

Color theory: level 1 (black) to 10 (lightest blonde); the law of color - primary (red, yellow, blue) mix to secondary (orange, green, violet); complementary colors neutralize (blue cancels orange, green cancels red, violet cancels yellow).

Developer volumes: 10 vol (3%) deposits only; 20 vol (6%) 1–2 levels lift with deposit; 30 vol (9%) 2–3 levels; 40 vol (12%) 3–4 levels and is used only on resistant, healthy hair. Off-the-scalp lighteners typically use 20 vol.

Patch test and predisposition test: required 24–48 hours before an aniline-derivative (oxidative) color service per manufacturer; record results. Strand test determines processing time and developer strength.

Skin: epidermis (stratum corneum, stratum granulosum, stratum spinosum, stratum germinativum/basal), dermis, subcutaneous. Fitzpatrick types I–VI guide waxing, peels, and laser suitability.

Facial treatments: cleanse, analyze, exfoliate, extract (steam to soften), massage, mask, moisturize, protect. Effleurage, petrissage, tapotement, and friction are the four massage movements; massage is contraindicated over inflammation, acne, or recent waxing.

Nails: nail plate, nail bed, cuticle (eponychium), lunula, matrix, free edge. Do not cut the eponychium; push back gently. Disinfect implements; single-use files and buffers.

Sanitation and infection control: bacteria (Staphylococci, Streptococci), fungi (tinea), viruses (HPV causes plantar warts). Disinfectants must be EPA-registered with a tuberculocidal claim; implements must be fully immersed per label contact time (often 10 minutes).