Hair and Hair Growth Cycles
The cycle
Hair grows in three phases: anagen (growth), catagen (transition/regression), and telogen (resting), followed by exogen (shedding). In anagen, the follicle is deepest and most vascular; the matrix cells divide actively. Catagen is brief, with the follicle shrinking and the papilla separating. Telogen holds a club hair until it sheds.
Understand hair types: vellus (fine, short, unpigmented), terminal (coarse, pigmented, deep), and intermediate. Hormones (androgens) drive conversion of vellus to terminal hair in androgen-sensitive areas. Recognize that only anagen hairs are optimally treatable; telogen hairs may require repeat treatment as they enter anagen.
Traps in questions
- Anagen is the growth phase, not the resting phase; questions often swap these.
- The deeper, vascular anagen follicle is more effectively treated but also more sensitive to current.
- Hair growth cycles differ by body site, so treatment intervals should reflect local cycle length.
- Shedding after treatment is normal and does not mean failure.
Rule of thumb
If a client asks why hair returns after a session, explain that hairs in telogen or catagen were not in the optimal growth phase and will need treatment when they re-enter anagen.