Anatomy and Physiology of Skin and Hair
Layers and structures
Know the epidermis (avascular, keratinized, renews from the basal layer), the dermis (collagen, elastin, blood vessels, nerves, glands, and the follicle's target zone), and the subcutaneous layer (fat, insulation, shock absorption). The follicle is a downgrowth of epidermis into the dermis; its bulge region (mid-follicle, insertion of the arrector pili) is the reservoir for epithelial stem cells, and the hair bulb/matrix at the base surrounds the dermal papilla, which supplies blood and signals growth.
Hair growth cycle
- Anagen: active growth; the follicle is deepest and most vascular; best target for effective epilation.
- Catagen: transitional regression; the follicle retracts and its blood supply dwindles.
- Telogen: resting; the club hair is shed and a new cycle begins.
Hair type matters: terminal hair is coarse, pigmented, and medullated; vellus is fine and unpigmented; lanugo is the fetal coat. Growth rate, density, and distribution are hormone-influenced (androgens), which is why treatment plans vary by site and client.
Traps to watch
- Confusing the bulge (stem-cell reservoir) with the bulb (matrix/papilla) - questions love this pair.
- Assuming all hair is in anagen; in reality follicles are asynchronous, which is why multiple sessions are needed.
- Believing the epidermis contains blood vessels (it does not; it is avascular).
- Forgetting that sebaceous glands empty into the follicle and that follicle anatomy affects treatment depth and infection risk.
Rule of thumb
Treat anagen, plan for the rest. Because only a fraction of follicles are in anagen at any time, schedule repeat sessions according to the growth cycle of the site, not a single-visit expectation.