6.1. Hair Structure and Growth Cycles
💡 First Principle: Hair removal doesn't just remove visible hair — it targets the follicle, which is the structure that produces new hair. Understanding the hair growth cycle explains why hair removal results vary, why multiple sessions are required for permanent methods, and which phase is relevant for which treatment.
Hair structure:
- Hair shaft — the visible portion above the skin surface
- Hair root — the portion below the skin surface, within the follicle
- Hair follicle — the tube-like structure in the dermis that anchors and produces the hair
- Hair bulb — the base of the follicle; contains the dermal papilla and the active growth cells
- Dermal papilla — supplies blood and nutrients to the follicle; must be destroyed for permanent removal
The hair growth cycle — three phases:
| Phase | Name | What's Happening | Relevance to Removal |
|---|---|---|---|
| Anagen | Active growth | Hair actively growing; follicle fully active; bulb connected to papilla | Best phase for laser/IPL — follicle is most active and laser energy is absorbed most effectively |
| Catagen | Transition | Hair growth stops; follicle begins to shrink | Short phase; not ideal for laser |
| Telogen | Resting | Hair fully detached from papilla; will shed naturally | Laser is ineffective — no connection to papilla |
Hair types:
- Vellus hair — fine, light, soft body hair (peach fuzz); not typically targeted for removal
- Terminal hair — coarser, pigmented, the hair on scalp, eyebrows, and most areas clients want removed
⚠️ Exam Trap: The anagen phase is optimal for laser and light-based methods — not for waxing. Waxing requires sufficient hair length to adhere to the wax, which is a length requirement (approximately ¼ inch), not a growth phase requirement.
Reflection Question: A client is undergoing laser hair removal and is frustrated that she needs multiple sessions. Using what you know about the growth cycle, explain why a single session cannot remove all hair permanently.
