How Does the Hair Growth Cycle Work? A Simple Guide

How Does the Hair Growth Cycle Work?
A Simple Guide

In our earlier articles, we covered why hair thins, what counts as normal shedding, and the main types of hair loss. But to really understand any of that, there's one piece of biology worth knowing first: hair doesn't grow continuously and indefinitely. Every strand follows a cycle, with clearly defined phases of growth, transition, and rest.

This isn't just a technical detail. It's the single most useful mental model for understanding almost everything about hair health, from normal shedding to why treatments take months to show results.

This guide breaks down the four phases simply, and points you to where you can go deeper on each one.

The Phases of the Hair Cycle

Anagen Phase (Active Growth)

• Cells at the base of the follicle multiply rapidly, forming the hair shaft
• Hair grows continuously, at roughly 1 centimeter (about 0.4 inches) per month
• Lasts anywhere from two to seven years, depending mostly on genetics
• Between 85% and 90% of your hairs are in this phase right now

→ Learn more: What Is the Anagen (Growth) Phase, and Why Does It Matter?

Catagen Phase (Transition and Regression)

• The follicle stops producing new cells and begins to shrink
• The hair detaches from the dermal papilla, the structure that nourishes the follicle
• The base of the hair transforms into a firmer structure known as a "club hair"
• Lasts only about two to three weeks
• Between 1% and 3% of hairs are in this phase at any given moment

→ Learn more: What Is the Catagen Phase? The Fastest Transition in the Hair Cycle

Telogen Phase (Follicle Rest)

• The follicle enters a state of complete biological rest
• The old hair stays anchored in the pore but no longer grows
• Lasts about three months, on average
• Between 9% and 15% of hairs are in this phase

→ Learn more: What Happens During Telogen, the Resting Phase?

Exogen Phase (Release and Shedding)

• More recent research treats shedding as its own subphase, distinct from telogen
• This is when the old hair finally releases from the scalp, which explains the 50 to 100 hairs we normally shed each day
• The follicle then restarts the process, re-entering anagen to produce a new strand

→ Learn more: What Is the Exogen Phase? Inside the Natural Shedding Mechanism

Beyond the Four Phases

Why does hair growth slow down over time?

Here's one of the most important connections to what we've covered before: in processes like androgenetic alopecia, the growth phase progressively shortens with each cycle, while the resting phase takes up proportionally more time. It's this imbalance, repeated cycle after cycle, that drives the progressive miniaturization of hair strands.

→ Learn more: Why Does Hair Growth Slow Down Over Time?

Can you speed up this cycle?

This might be the most practical question of all, and the answer has a direct implication for treatment expectations: since every phase of the cycle has its own biological duration, no approach can "skip steps." Understanding this is essential for not falling for promises of results in just a few days.

→ Learn more: Can You Speed Up Your Hair Growth Cycle?

The Doctor Prime Perspective

Understanding the hair cycle changes the question that's actually worth asking. Instead of "why is my hair falling out," the more useful question becomes: "is my hair cycle behaving the way it should?"

That shift in perspective guides everything we publish, and it's exactly why we've dedicated an entire series to explaining this mechanism before talking about any solution.

Selected References:
NCBI Bookshelf (NIH), StatPearls: Anatomy, Hair
PMC / National Library of Medicine (NIH), Using the Mechanisms of Action Involved in the Pathogenesis of Androgenetic Alopecia to Treat Hair Loss
Healthline (medically reviewed), Stages of Hair Growth Plus How to Maintain Hair Health in Every Stage
PubMed, The Role of Variations in Growth Rate and Sample Collection on Interpreting Results of Segmental Analyses of Hair
PMC / National Library of Medicine (NIH), Integrative and Mechanistic Approach to the Hair Growth Cycle and Hair Loss
PMC / National Library of Medicine (NIH), Exogen Hairs in Women with and without Hair Loss