Hair fibre, growth and material behavior
Hair-service decisions require a distinction between the living follicle and the fibre extending from it. New cells are produced in the growing follicle; the visible shaft is largely keratinized material. The cuticle forms an overlapping protective outer structure. The cortex contributes much of the fibre's strength, elasticity and pigment. A medulla may be present, particularly in coarser fibres, but it is not a required central tube in every hair. A conditioner improving feel does not make an already emerged shaft biologically grow back to an undamaged state.
Natural pigment involves different types and distributions of melanin. Eumelanin contributes brown and black tones, while pheomelanin contributes warmer red and yellow tones. The visible appearance also depends on fibre arrangement, lighting and prior treatment. Gray hair is not one uniform processing category. Assess the particular fibre and history instead of assuming that every gray or curly strand has identical porosity or resistance.
Keratin structure involves several kinds of interactions. Hydrogen-bond rearrangement helps explain temporary wet-setting and thermal styling. Disulfide links between cysteine residues contribute to more durable structure. Chemical waving and hydroxide relaxing do not use an identical reaction pathway, and processing one does not authorize combining it with the other. pH can affect fibre swelling and product behavior, but a pH number alone does not specify a whole formulation, its compatibility or its safe contact time.
Porosity concerns how a fibre takes up and retains water or products; previous lightening and damage can create uneven behavior along one length. Elasticity concerns extension and recovery under stated conditions. Neither observation independently diagnoses a scalp disorder. Use product-specified assessment methods without stretching weakened hair to the point of injury or treating a single quick check as permission for any chemical service.
Growth proceeds through active, transitional and resting phases, with shedding associated with the cycle. Individual follicles do not all occupy the same phase simultaneously. Hair loss, broken fibres and scalp inflammation have different possible causes. Record observations, ask relevant history and keep cosmetic service within competence. Unexplained patches, sores or suspected infection need appropriate assessment rather than a stylist's confident diagnosis or medication recommendation. This teaching explains material and biological foundations, not a universal timetable, chemical formula or medical treatment.