◆ IDUN Journal

The Four Phases of Hair Growth, Explained

By Siu Lie Tan, Founder · 5 min read

Every hair on your head is somewhere in a four-act cycle. Knowing the acts explains almost everything about growth.

Hair does not grow at a steady, uniform pace. Each follicle moves independently through a repeating cycle of four phases — which is why you are always both growing and shedding at once, and why patience is not optional but structural.

1. Anagen — the growth phase

The active phase, when the follicle builds hair from the root and pushes it steadily longer. Anagen lasts years — commonly two to six — and at any moment around 85–90% of the hairs on a healthy scalp are in it. The length of your anagen phase is what sets how long your hair can ultimately grow. Nutrition, circulation and inflammation all influence how well, and how long, a follicle sustains this phase.

2. Catagen — the transition

A brief bridge of a few weeks. The follicle detaches from its blood supply and shrinks, and the hair becomes a "club" hair. Only a small fraction of follicles sit here at any time. It is the quiet turning point between building and resting.

3. Telogen — the rest

A resting phase of roughly three months, during which the club hair sits dormant while a new hair begins to form beneath it. Around 10–15% of hairs are resting at any given time. When a shock pushes an unusually large group of follicles into telogen at once, the coordinated shedding that follows months later is what dermatologists call telogen effluvium.

4. Exogen — the shedding

The natural release of the old hair so the new one can emerge — the source of the 50 to 100 hairs a healthy person loses each day. Exogen is not loss in the worrying sense; it is turnover, the cycle beginning again.

Why the timing of care matters

Two truths follow from the cycle. First, results are never instant: because visible hair is the output of a months-long process, any genuine support shows up on the scalp’s timeline, not the calendar you would prefer. In IDUN’s testing, the first signs of new growth appeared by week four, with density up an average of 10.71% — early, but still measured in weeks.

You are not styling a finished object. You are tending a process already in motion.

Second, consistency beats intensity. Because follicles are each at a different point in the cycle, support applied daily reaches them across all their phases over time; support applied in occasional bursts misses most of them. This is the quiet argument for a daily ritual rather than an intensive weekend — and the reason 001 is designed to be used every day, a few unhurried minutes at a time.

This article is for general educational purposes and is not medical advice. IDUN's cited results (+18.04% skin elasticity, +10.71% hair density at four weeks) reflect IDUN's own product testing. For a medical concern, consult a qualified professional.