Hair Structure and Growth Patterns
Hair Structure and Growth Patterns
Understanding how hair is built and how it grows is the foundation of every great haircut. Before you pick up a pair of scissors, knowing what you're cutting β and why it behaves the way it does β will dramatically improve your results.
The Anatomy of a Hair Strand
The human hair is composed of three main parts: the hair shaft, the hair bulb, and the hair follicle. Each plays a distinct role:
- Hair Shaft: The hair shaft is a thin, flexible cylinder of non-living, keratinized epithelial cells visible above the epidermis. This is the part you actually cut.
- Hair Follicle: The hair follicle is a tiny, tube-like structure in the skin from which each hair strand grows.
- Hair Bulb: The hair bulb is the region of the follicle that actively produces hair, extending into the dermal layer and surrounding the dermal papilla β a structure supplied by capillaries that deliver nutrients.
The Three Layers of the Hair Shaft
Hair is made up of three distinct layers: the medulla, cortex, and cuticle.
- Cuticle: The outermost layer, consisting of overlapping scales that protect the inner layers of the hair. When the cuticle is smooth and flat, hair appears shiny and healthy.
- Cortex: The cortex plays a vital role in determining the physical and mechanical properties of the hair, such as strength, texture, and color. Split ends expose the cortex β worn away by harsh treatment. Without the cuticle, the fibers of the cortex fray like the strands of a rope, and since the cortex can't heal itself, the only remedy is to cut them off.
- Medulla: The medulla is a central core of loosely arranged cells, often absent in fine hair.
Hair Texture and Shape
Hair texture β whether straight or curly β is determined by the shape and structure of the cortex and medulla, which are in turn determined by the shape of the hair follicle. This is why you can't permanently change natural curl pattern with cutting alone.
The Hair Growth Cycle
Hair follicles undergo a cyclical process comprising growth (anagen), regression (catagen), rest (telogen), and shedding (exogen) β a cycle essential for continuous hair renewal.
- Anagen (Growth Phase): The growth phase can last 2 to 6 years for scalp hair and only a few months for eyebrows and eyelashes.
- Catagen (Transition Phase): The catagen phase lasts only a few weeks and is the shortest phase; cell division in the matrix ceases during this time.
- Telogen (Rest Phase): During the telogen phase, the hair follicle is at rest and no new growth occurs; this phase lasts about 2 to 4 months before another anagen phase begins.
Hair typically grows at the rate of 0.3 mm per day during the anagen phase β roughly half an inch per month β which is useful knowledge when advising clients on trim schedules.