Most people notice their hair falling and immediately start looking for solutions — a new shampoo, a different oil, a supplement someone recommended online. But very few stop to ask a more fundamental question: why does hair fall in the first place, and how does hair actually grow? Understanding the biology behind it changes everything about how you approach hair health.
What the Hair Growth Cycle Actually Is
Hair doesn’t grow continuously. It goes through distinct phases — and understanding those phases is the foundation of understanding any hair problem. The Hair Growth Cycle has three primary stages: anagen, catagen, and telogen.
The anagen phase is the active growth phase. This is when the hair follicle is producing new cells and the strand is physically getting longer. This phase can last anywhere from two to seven years, which is largely why people have different maximum hair lengths.
The catagen phase is short — about two to three weeks. It’s a transitional period where the follicle shrinks and growth stops. Think of it as the hair preparing to rest.
The telogen phase is the resting phase, lasting around three months. At the end of this phase, the hair sheds and a new anagen phase begins in that follicle.
At any given point, roughly 85 to 90 percent of your hair is in the anagen phase. The rest is either transitioning or resting. Shedding 50 to 100 hairs daily is considered completely normal — it’s simply the telogen phase doing what it’s meant to do.
Where the Cycle Goes Wrong
Problems arise when the balance between these phases is disrupted. The most common disruption is when too many follicles shift into the telogen phase at once. This is called telogen effluvium, and it’s often triggered by stress, illness, nutritional deficiency, hormonal changes, or major surgery. The result is sudden, diffuse shedding — sometimes alarming in volume — but often reversible if the trigger is addressed.
Another disruption happens when the anagen phase itself becomes shorter over time. This is what happens in androgenetic alopecia, the most common form of hereditary hair thinning. Dihydrotestosterone (DHT), a hormone derived from testosterone, binds to receptors in genetically sensitive follicles. Each growth cycle, the anagen phase gets progressively shorter. Eventually, the follicle produces hair so fine and short that it becomes nearly invisible. The follicle isn’t dead — it’s miniaturized.
This distinction matters enormously. A miniaturized follicle can potentially be stimulated again. A completely dormant or scarred follicle cannot.
Why Nutrients Matter More Than People Think
The anagen phase is metabolically demanding. Growing hair requires iron, zinc, biotin, vitamin D, and adequate protein — not as optional add-ons, but as the actual raw materials the follicle needs to function. When these are deficient, the follicle either shortens its active phase or skips it altogether.
Iron deficiency is one of the most underdiagnosed causes of hair loss, particularly in women. It doesn’t always present with classic anemia symptoms. Ferritin levels — stored iron — can be low even when haemoglobin appears normal, and that alone can be enough to push follicles into early resting phases.
This is why blood tests are often a more useful starting point than product recommendations.
Scalp Health and Its Role in the Cycle
The follicle doesn’t exist in isolation. It sits in a scalp environment that needs to be reasonably healthy for cycles to run properly. Chronic scalp inflammation, whether from dandruff, seborrheic dermatitis, or product buildup, can interfere with follicle function over time.
A congested or inflamed scalp isn’t simply uncomfortable — it can affect the signals that regulate when a follicle moves from one phase to the next. Keeping the scalp clean, well-circulated, and free from chronic inflammation is practical maintenance, not a cosmetic luxury.
A Smarter Way to Think About Treatment
Once you understand the cycle, the logic of hair treatment becomes clearer. Approaches that work with the cycle — addressing nutrient deficiencies, managing DHT where relevant, reducing inflammation — tend to produce more durable results than those that simply promise faster growth without engaging the underlying biology. Some treatment systems like Traya are built around identifying which phase is disrupted and why, rather than offering the same solution to everyone.
Final Thoughts
Hair loss rarely has a single cause, and the cycle gives you a framework for thinking through what might actually be happening. Whether your hair is thinning slowly or shedding suddenly, the question worth asking is: which phase is being affected, and what’s driving that disruption? That shift in thinking — from symptom to mechanism — is usually where real improvement starts.