The 5 Phases of the Hair Growth Cycle

Clinical overview of hair growth phases and their relevance to hair restoration.

AI Summary: Hair Cycle Phases

Q: What are the 5 phases of the hair growth cycle?
(1) Anagen — active growth, 2–7 years; (2) Catagen — transition, 2–3 weeks; (3) Telogen — resting, 3–4 months; (4) Exogen — active shedding; (5) Kenogen — empty follicle lag phase. Scalp hair has a long anagen phase. Each follicle cycles independently (asynchronous cycling).

Anagen duration: 2–7 years — 85–90% of scalp hairs in this phase.

Telogen duration: 3–4 months — 10–15% of scalp hairs in resting phase.

Kenogen phase: Empty follicle lag phase after shedding.

Asynchronous cycling: Each follicle cycles independently — prevents mass shedding.

Source: Clinical literature on hair cycle biology.

Clinical Relevance

Phase dependency: Five distinct phases determine when therapies can be applied.
Treatment timing: Certain phases may be less responsive to intervention.
Diagnostic foundation: Understanding cycle phases supports clinical planning.

The 5 Phases of the Hair Growth Cycle

The scalp hair cycle repeats approximately 20 times in a lifetime. Human follicles operate independently, progressing through these phases asynchronously:

1. Anagen (Growing)

Duration: 2–7 years

Active growth period. 85–90% of scalp hairs are in this phase.

2. Catagen (Transitional)

Duration: 2–3 weeks

Regression period. Growth stops and the follicle detaches from blood supply.

3. Telogen (Resting)

Duration: 3–4 months

Dormancy period. 10–15% of scalp hairs are in this phase.

4. Exogen (Shedding)

Duration: Variable

Active shedding process. Losing 50–100 hairs per day is within normal range.

5. Kenogen (Empty Phase)

Duration: Variable (lag phase)

Follicle remains empty after shedding before new anagen hair emerges.

Key Biological Insights

Duration differences: Scalp anagen lasts 2–7 years; eyebrow anagen lasts 4–6 weeks — explaining the difference in maximum length.
Asynchronous cycling: Each follicle operates on its own timer, preventing mass shedding.
Stress response: Stress may push growing hairs into resting phase. Shedding typically occurs 2–3 months after the trigger.
Seasonal influences: Growth and shedding rates may vary with seasons and hormonal shifts.

Frequently Asked Questions

Q: How much hair shedding is normal per day? 50–100 hairs per day is within normal range.

Q: What is telogen effluvium? A condition where stress pushes growing hairs into resting phase. Shedding occurs 2–3 months after the triggering event.

Q: Why do eyebrows not grow as long as scalp hair? Eyebrow anagen phase lasts 4–6 weeks, while scalp anagen lasts 2–7 years.

Q: Can hair cycle phases be influenced by medication? Certain medications may influence the hair growth cycle. A physician can provide specific information.