Hair and scalp
The anatomy of scalp skin consists of three layers:
Epidermis: This is composed of five sub-layers – the basal cell layer, the squamous cell layer, the stratum granulosum, the stratum lucidum, and the outermost stratum corneum.
Dermis: A connective tissue that supports the epidermis with its abundance of elastic collagen fibres. Rich in blood vessels, the dermis provides nourishment to the epidermis.
Hypodermis: Very similar to the dermis, but characterized by fat cells.
In addition to the hair on the majority of our body surface, our skin also contains the sweat and eccrine glands, and the vascular system.
The hair shaft itself is composed of three main areas:
- the cuticle
- the cortex
- the medulla
The hair growth cycle is marked by three phases: the anagen, catagen and telogen phases.
Anagen Phase: This is the active phase of hair growth in which new hair is formed. The average anagen growth phase is between three and seven years. The phase is longer for women.
Catagen Phase: The follicle undergoes a transitional phase and the outer root sheath shrinks. Shorter than the anagen phase, the catagen phase generally lasts for about a month.
Telogen Phase: This is the stage preceding hair loss, during which the hair follicle detaches and then falls out. This phase lasts between three and four months and is then followed by the regrowth of the hair and the renewal of the anagen cycle.