What Is the Exogen Phase? Inside Natural Hair Shedding

What Is the Exogen Phase?
Inside the Natural Shedding Mechanism

We've already talked, in earlier articles, about how many hairs are normal to lose in a day. But there's a question we haven't answered directly yet: what actually happens, biologically, at the moment a hair releases from the scalp? The answer lies in the most recently recognized phase of the hair cycle: exogen.

What is the exogen phase?

For a long time, shedding was treated as simply the final part of telogen, the resting phase. But more recent research proposes that there's a distinct phase dedicated specifically to the release process itself: exogen.

Under this framework, exogen is defined as the point where the signals for hair release are given, and the release process is actually carried out, ending once the hair is fully detached. In other words, a hair can technically be "ready to fall" during part of telogen, but it's only during exogen that the shedding actually happens.

How does this connect to the number of hairs we lose per day?

This is exactly the mechanism behind the 50 to 100 hairs that, as we've covered before, are considered normal in a day. Each of those hairs is passing through the exogen phase at that specific moment, while thousands of others are in completely different stages of the cycle.

One detail worth noting: shedding is often assisted by everyday actions like washing and brushing. That doesn't mean these actions are "pulling out" healthy hair; they simply help release strands that were already ready to go, a process that would happen either way, sooner or later.

What happens after the hair falls out?

Exogen marks the end of one cycle and, at the same time, the start of the next: as soon as the old hair releases, the follicle restarts the process, re-entering the anagen phase to produce a new strand. This ties back to something we mentioned in our article on telogen: new growth, in many cases, is already forming underneath the old hair before it even falls out.

Why does this phase matter for understanding conditions like telogen effluvium?

Researchers studying the exogen phase also use this concept to better understand conditions like telogen effluvium and androgenetic alopecia. By examining the ratio of hairs in early telogen, full telogen, and exogen, it's possible to identify patterns that help distinguish what's actually happening in each case. That shows that, even as a relatively recent concept in hair research, the exogen phase has real clinical application, not just theoretical distinction.

What This Means for You

Finding hair on your pillow, in your brush, or in the shower drain is, in practice, you witnessing the exogen phase in action, a natural, expected process, not a sign of a problem on its own. What's worth watching for, as we've discussed before, isn't the presence of those hairs, but real changes in pattern over time.

FAQ

Is the exogen phase the same thing as telogen?
Not exactly. Classically, shedding was treated as the final part of telogen, but more recent research treats exogen as its own phase, focused specifically on the hair release process.

Does washing or brushing "cause" shedding during the exogen phase?
Not in the sense of causing damage. These actions help release hairs that were already ready to come out, but they don't pull out healthy hairs that are still firmly anchored.

The Doctor Prime Perspective

The exogen phase closes the loop we've explored throughout this series: growth, transition, rest, and finally, release. Understanding this full sequence is what turns the anxiety around "finding strands" into a calmer, evidence-based understanding of how hair actually works.

Continue reading: Why Does Hair Growth Slow Down Over Time?

Selected References:
PMC / National Library of Medicine (NIH), Exogen Hairs in Women with and without Hair Loss
Healthline (medically reviewed), Stages of Hair Growth Plus How to Maintain Hair Health in Every Stage
NCBI Bookshelf (NIH), StatPearls: Anatomy, Hair