Hair Care and Hair Services
Structure, growth, and analysis
Hair has three layers: the cuticle (overlapping scales), the cortex (the bulk of the fiber, where melanin lives), and the medulla (a core that may be absent). Growth cycles are anagen (active, lasting years), catagen (transition, weeks), and telogen (resting and shedding, months). Hair analysis covers texture, density, porosity (how readily the hair absorbs moisture), elasticity (stretches and returns without breaking), and growth pattern. Poor elasticity is a stop sign for chemical services.
Services and the chemistry behind them
Shampooing and scalp massage, conditioning, cutting, thermal styling, haircolor, permanent waving, relaxing, and hair additions each carry their own safety tests. Haircolor levels run from 1 (black) to 10 (lightest blonde). Developer volumes are commonly 10, 20, 30, and 40, corresponding to roughly 3%, 6%, 9%, and 12% hydrogen peroxide. Aniline-derivative tints require a predisposition (patch) test 24 to 48 hours before the service, and a strand test predicts processing.
Permanent waves and relaxers work through the same chemistry: they break disulfide bonds and then reform them. Thioglycolate acid waves have a low pH; alkaline waves swell the hair more. Sodium hydroxide relaxers are high-pH lye products; guanidine hydroxide is the no-lye alternative; ammonium thioglycolate is the low-pH thio relaxer used for fine or color-treated hair.
Traps and a rule of thumb
Exams confuse developer volume with color level, and they imply that waving and relaxing are unrelated processes; both are disulfide-bond chemistry. For relaxer retouches, apply product to the new growth first and pull through only for the final few minutes. Rule of thumb: test before you treat - patch test, strand test, and elasticity check are the three habits that prevent most chemical disasters.