The hair growth cycle is the process every strand on your head moves through, on repeat, for life. Once you know how it works, it's much easier to tell normal shedding apart from real hair loss - and what you can do about it.
How Hair Grows
Each strand of hair grows from a hair follicle embedded deep in your scalp. At its base, the hair bulb surrounds the dermal papilla, which feeds nutrients and oxygen to matrix cells - some of the fastest-dividing cells in the body[1] (this is partly why chemotherapy causes - the drugs target the body's fastest-dividing cells, and hair cells fall into that category right alongside tumor cells). As matrix cells multiply, older cells are pushed upward and harden into keratin, forming the hair shaft. The hair that you can see is technically dead tissue; all the key biological activity happens below the surface.
What’s most important is that your roughly 100,000 scalp follicles don't grow in sync. Each runs on its own independent cycle. This "mosaic" pattern is why you don't go bald instantly overnight, and why finding hair in your brush each day is expected, not alarming. Unlike animals that molt in sync, humans shed follicle by follicle, continuously.
The Four Phases of the Hair Cycle
Anagen (growth):
Anagen is the active phase of hair growth, lasting 2-6 years on the scalp (much shorter elsewhere on the body, e.g., thigh hair grows for only about 2 months, which is why body hair never gets super long). Approximately 85-90% of scalp hairs are in the anagen phase at any given time. Your genetics largely determine how long this phase runs, which is why some people's hair grows much longer than others.
Catagen (transition):
Catagen is a short, 2–3 week phase where hair stops growing, the hair follicle shrinks, and subsequently detaches from the blood supply. The hair shaft becomes a "club hair." Only 1-3% of follicles are in this phase at once.
Telogen (rest):
The hair follicle goes dormant - anywhere from a few weeks (body hair) to up to a year (scalp hair). About 10-15% of scalp hairs are resting in telogen at any time[2]. Near the end, a new anagen phase quietly begins underneath, driven by reactivated stem cells in the hair follicle's "bulge" region.
Exogen (shedding):
The old club hair releases and falls out, usually nudged loose by washing or brushing, or displaced by the new hair growing beneath it. Losing 50-100 hairs a day this way is normal and gets replaced automatically.
Scalp hair grows about one inch every two months, and a single follicle cycles through this whole process roughly 25-30 times over a lifetime.
Normal Shedding vs. Hair Loss
In most cases, hair shedding without follicle damage is reversible. Hair can fall out under stress (such as in the case of Telogen Effluvium), but miniaturized or scarred follicles are a tougher problem.
- Normal shedding: ~50-100 hairs lost daily via exogen, each replaced by a new hair from the same follicle. Density stays stable.
- Hair loss: The hair cycle itself is disrupted - hair follicles shed excessively, spend less time in anagen, or stop producing hair altogether. A visible decline in density is observed over time.
What Disrupts the Cycle
Androgenetic alopecia (pattern hair loss) is the most common cause, driven by genetic sensitivity to DHT (a testosterone byproduct). In susceptible follicles, DHT shortens anagen and shrinks the follicle over successive cycles - a process called follicular miniaturization. In men, this typically shows up as a receding hairline and thinning crown; in women, it more often presents as diffuse thinning along the part line rather than a receding hairline, and isn't driven by androgens alone. Early treatment tends to work better than waiting.[3]
Telogen effluvium happens when a major stressor, such as illness, surgery, childbirth, crash dieting, high fever, or nutrient deficiency, pushes many follicles into telogen at once[4]. Because they shed together roughly 2-3 months later, the connection to the original trigger is often missed. Postpartum shedding is a common, temporary example. The hair follicles themselves aren't damaged, so hair usually regrows within 6-9 months. Anagen effluvium disrupts hair mid-growth, most often from chemotherapy, causing faster, more dramatic loss - but that’s usually reversible once the treatment ends. Alopecia areata is autoimmune: the immune system attacks anagen-phase follicles, causing sudden patchy loss. Follicles typically stay intact, so regrowth is possible, though unpredictable. Traction alopecia, from tight hairstyles, braids, or extensions, and certain medications (blood thinners, some antidepressants, beta-blockers, retinoids) can also disrupt the hair cycle.
Supporting a Healthy Hair Cycle
The key to supporting a healthy hair cycle is to prioritize removing core stressors of the hair follicle while identifying and supporting key gaps. This is what we recommend:
- Check for nutrient gaps - iron/ferritin, vitamin D, zinc, and thyroid function are worth testing if shedding increases.
- Treat common scalp conditions like dandruff or seborrheic dermatitis, which are linked to oxidative stress that can affect follicles.
- Go easy on styling - heat, chemical processing, and tight hairstyles contribute to breakage and traction alopecia.
- Manage stress, a well-documented trigger for hair loss.
Restarting a Disrupted Cycle
For many situations, resolving the underlying trigger is usually enough. For androgenetic alopecia, the two FDA-approved, most-studied options are:
- Minoxidil (topical) — prolongs anagen and enlarges miniaturized follicles.
- Finasteride (oral, prescription, for men) — blocks DHT conversion, slowing miniaturization. Does not work well for female androgenetic alopecia.
These treatments work best on follicles that are still alive, even if they have become significantly smaller. Areas that have been completely bald for years may have limited capacity to respond, which is one reason earlier intervention can matter. And because the hair cycle is slow, most treatments typically require 3-6 months of consistent use before meaningful changes become apparent.
RE:YOU's proprietary NOVOGRO™ technology takes a different approach. Rather than targeting DHT or relying on minoxidil, it is designed to support the biology of the follicle itself while simultaneously nourishing the surrounding scalp environment. RE:YOU’s Dual-Path Hair Revival Serum helps create the optimal conditions that may help weakened and miniaturized follicles produce stronger, more visible hairs over time.
When to See a Dermatologist
If you notice sudden or patchy hair loss, heavy shedding lasting more than 3–6 months, scalp redness or scaling, or hair loss alongside other symptoms like fatigue or irregular periods, reach out to your dermatologist. A dermatologist can perform a pull test, scalp examination, or other evaluation to distinguish a temporary disruption from more persistent changes to hair follicle health.
FAQ
- How many hairs is normal to lose per day? About 50-100, as part of the normal shedding process.
- How long is a full hair growth cycle? Roughly 2-6 years on the scalp, though it varies by person and hair follicle.
- How fast does hair grow? About half an inch per month, or roughly six inches per year.
So can a disrupted hair cycle be reversed?
Often, yes - but it depends on why the cycle was disrupted and whether the hair follicle is still viable. Some situations may resolve themselves once the underlying trigger is addressed. Pattern hair loss is more complex, but early intervention can slow hair follicle miniaturization and, in some cases, help restore hair density. The key thing to remember is that hair loss isn’t irreversible. A hair follicle that is producing thinner, weaker hairs may still have enough biological activity for visible regrowth. The challenge is understanding why that follicle has changed - and finding the right way to support it.
