ND Barber cheat sheet

Anatomy of the hair follicle: infundibulum (surface to sebaceous duct), isthmus (sebaceous duct to arrector pili insertion), and inferior segment (bulge to bulb); the bulge houses the epithelial stem cell reservoir.

Hair growth cycle: anagen (2-7 years, active growth), catagen (2-3 weeks, regression), telogen (about 3 months, resting), exogen (shedding); roughly 85-90% of scalp hairs are in anagen at any time.

Hair shaft layers from outside in: cuticle (overlapping scales), cortex (keratin filaments and melanin), medulla (central, may be absent in fine hair).

Disulfide bonds between cysteine residues give hair its tensile strength and are the target of chemical relaxers; hydrogen bonds are broken by water and reset by heat and drying.

Melanin types: eumelanin (brown-black) and pheomelanin (red-yellow); graying reflects declining melanocyte activity in the bulb, not loss of keratin.

Skin layers: epidermis (stratum corneum, granulosum, spinosum, basale), dermis (collagen, elastin, follicles, glands), hypodermis (subcutaneous fat).

pH reference: scalp skin surface about pH 4.5-5.5; hair shaft swells and the cuticle lifts as pH rises, which is why alkaline products increase porosity and friction.

Normal scalp shedding is commonly cited as 50-100 terminal hairs per day; sudden diffuse shedding warrants medical referral rather than cosmetic treatment.

Patchy, well-demarcated hair loss with smooth skin and exclamation-point hairs suggests alopecia areata; refer, since it is autoimmune and not a barbering condition.

Diffuse thinning along the frontal hairline and crown with miniaturization and family history suggests androgenetic alopecia; document pattern and refer for medical confirmation.

Scarring (cicatricial) alopecia shows absent follicular ostia and shiny skin; it is irreversible and requires dermatologic referral before any chemical service.

Traction alopecia presents with marginal thinning at temples and nape, often with folliculitis or broken hairs; identify tight braids, weaves, or repeated tension as the cause.

Fungal scalp infection (tinea capitis) signs: scaling, broken hairs at scalp level, black-dot appearance, possible lymphadenopathy; do not treat cosmetically, refer.

Seborrheic dermatitis versus psoriasis: seborrheic scale is greasy and yellow with mild erythema; psoriasis plaques are silvery, well demarcated, and may extend beyond the hairline.

Contraindications to chemical service include open lesions, recent scalp surgery, active infection, known PPD allergy, and pregnancy-related physician restriction.

Patch testing 24-48 hours before first application of oxidative dye or relaxer is the standard screen for allergic contact dermatitis.

Chemical relaxer pH is typically 12-14 (lye, sodium hydroxide) or no-lye (guanidine hydroxide, calcium hydroxide plus activator); both require strand test and scalp protection.

Relaxer timing rule: process by visual smoothing check at intervals, never exceed manufacturer maximum, and do not apply to scalp that has been scratched or chemically irritated within 48 hours.

Oxidative dye development: permanent color uses aniline derivatives plus developer; volume strength sets lift - 10 vol (3%) deposit, 20 vol (6%) one level lift, 30 vol (9%) two to three levels, 40 vol (12%) maximum lift with higher risk.

Bleach lightening follows the same oxidative principle; do not exceed manufacturer on-scalp time and never overlap previously lightened hair without a porosity check.

Patch test and strand test are separate steps: patch test screens allergy, strand test predicts timing, lift, and integrity on the actual hair.

Neutralizing after a thioglycolate perm rebuilds disulfide bonds and lowers pH; incomplete neutralization leaves hair limp and over-elastic.

Treatment plan sequence: assess scalp and hair, identify contraindications, patch and strand test, then schedule service with aftercare instructions in writing.

Keratin smoothing treatments are not the same as relaxers; they coat and temporarily straighten via heat and are not a substitute for chemical straightening when true texture change is requested.

Para-phenylenediamine (PPD) is the primary sensitizer in permanent hair dye; cross-reactivity occurs with related aromatic amines such as PTD and some tattoo inks.

Henna (lawsone) is a plant dye that binds keratin; pure henna does not lighten hair, and 'black henna' often contains added PPD, raising sensitization risk.

Essential oils used in scalp products (tea tree, peppermint, rosemary) can cause contact dermatitis; dilute per manufacturer and patch test.

Minoxidil is a topical vasodilator for androgenetic alopecia; barbers may encounter it but must not advise on dosing or discontinue prescribed therapy.

Prescription 5-alpha reductase inhibitors (finasteride) reduce DHT; clients should be directed to their prescriber for questions about effects and handling precautions.

Thioglycolate salts (ammonium thioglycolate) break disulfide bonds in perms and depilatories; they are incompatible with oxidative dyes applied in the same session.

Ammonium persulfate is the booster in bleach; it is a known respiratory and skin irritant, so mix in ventilated areas and avoid inhalation.

Botanical claims are not proof of safety; verify concentration, source, and allergen statement on the label before applying any plant-derived product.

Iron deficiency is a common reversible cause of diffuse hair shedding; ferritin and hemoglobin are the relevant labs and interpretation belongs to the clinician.

Telogen effluvium often follows illness, surgery, severe dieting, or childbirth by about 2-3 months; the trigger timeline is the key history question.

Protein-energy malnutrition reduces hair diameter and growth; keratin is protein, so adequate intake matters, but supplements do not regrow hair without a deficiency.

Thyroid dysfunction and untreated diabetes can affect hair and skin; refer for evaluation rather than recommending supplements.

Smoking and high ultraviolet exposure are associated with premature graying and photoaging of scalp skin.

Traction and friction from tight styles, harsh brushing, and heat tools are modifiable lifestyle factors that barbers can address directly.

Counseling scope: provide general wellness information and refer; do not diagnose deficiency, prescribe supplements, or interpret laboratory results.

Documentation of advice given (heat protection, cleansing frequency, tension reduction) supports continuity and defends against later disputes.

Licensure is state-specific: scope of practice, sanitation rules, and continuing education hours are set by the state board, not by the school or product brand.

Informed consent for chemical services means disclosing risks such as breakage, allergic reaction, and unpredictable color result, and recording the client's agreement.

Client records should capture service date, products and batch, patch and strand test results, and any adverse reaction.

Confidentiality covers health information and images; do not post client photos without written permission.

Universal precautions: gloves for chemical and blood exposure, handwashing, single-use blades and neck strips, and disinfection of clippers and shears per state rule.

Never diagnose or treat disease; scope of practice is cosmetic, and suspected skin or scalp disease is referred to a physician.

Pricing and disclosure: quote before service, itemize add-ons, and state cancellation policy in writing to avoid disputes.

Insurance and liability: maintain general liability coverage, keep SDS sheets accessible, and follow manufacturer mixing ratios as a defense against negligence claims.

Clipper blade numbers: lower numbers cut closer; a #1 leaves about 1/8 inch, #2 about 1/4 inch, #3 about 3/8 inch, #4 about 1/2 inch, before guard or lever adjustment.

Guard comb numbering follows the same eighth-inch increment convention as blade numbers.

Fade mechanics: establish the shortest guide at the nape or sides, then blend upward by opening the lever and stepping through guards to remove lines.

Shear cutting angles: blunt or one-length cuts follow the head curve; graduated and layered cuts elevate hair at consistent angles for predictable length distribution.

Razor cutting slices the cuticle and produces softer texture but increases porosity; avoid on fine or previously lightened hair.

Cross-checking means cutting the section a second time perpendicular to the first to verify balance and symmetry.

Taper versus fade: a taper shortens only at the perimeter with a visible weight line; a fade blends gradually with no line.

Sanitation for barbering tools: clipper blades cleaned of hair and debris, then disinfected with an EPA-registered hospital-grade product per label contact time.

Shampoo selection by scalp condition: oily scalp needs more frequent cleansing with a mild surfactant; dry scalp needs less frequent washing and lower surfactant intensity.

Conditioner acts on the cuticle: cationic surfactants and silicones reduce friction, smooth scales, and lower static; apply mid-shaft to ends, not the scalp.

Porosity test (float test) is a rough indicator only; a reliable assessment is how quickly hair absorbs water and product and how it feels when wet.

Elasticity test: wet a strand and stretch; normal hair extends about 30% and returns, while over-processed hair stretches further and does not recoil.

Protein treatments fill gaps in the cortex temporarily; moisture treatments restore hydration - overuse of protein on low-porosity hair causes stiffness and snapping.

Scalp massage and cleansing reduce buildup of sebum and product residue; medicated shampoos for dandruff contain zinc pyrithione, selenium sulfide, or ketoconazole and are used per label.

Heat protection: keep irons and dryers within manufacturer temperature guidance and avoid applying high heat to wet, fragile, or chemically lightened hair.

Aftercare for relaxers and color: wait the manufacturer-recommended interval before the next chemical service and use sulfate-free, pH-balanced cleansers to limit cuticle stress.