Anagen, Catagen, Telogen: The Hair Cycle, Properly Explained

By Dr. Susan Lin, MD | MD HAIR | La Cañada Ventures, Inc.
Published on mdhair.com — Verbascoside & Lilac Science Series

You counted them. Not on purpose, the first time — you just noticed how many were in the shower drain and something in you decided that number was information. Now you count most days. Some mornings it is thirty and you feel fine. Some mornings it is ninety and the rest of the day has a shadow over it.

Here is the first thing I want you to know, and it will not sound like reassurance until you have read the rest of this article: the hairs you counted this morning stopped growing about three months ago. Whatever they are telling you about, it is not today. It is late winter, or that fortnight of illness, or the six weeks when you were not eating properly. The drain reports on the past.

That single fact — a three-month reporting delay built into your own scalp — is the reason so much hair-loss advice is wrong, so much panic is misdirected, and so many products are judged on a timescale on which nothing could possibly have happened yet.

I am Dr. Susan F. Lin, M.D. — Boston University School of Medicine, board-certified in Obstetrics & Gynecology and in Anti-Aging Medicine, and the physician who has formulated the MD® line at La Cañada Ventures, Inc. since 2008. This is the reference article for this site: the piece everything else links back to when it says the hair cycle. I have tried to make it the version I wish existed when patients asked me.

Three Phases, and a Fourth Most Articles Omit

Every hair follicle on your body runs a repeating programme. It grows a hair, dismantles the machinery that grew it, rests, and starts again. Each follicle runs its own copy of that programme on its own schedule.

Anagen — the growth phase

Anagen is when the follicle is actively building a hair. The bulb is deep in the dermis, the matrix cells above the dermal papilla are dividing as fast as almost any cell population in the human body, melanocytes are loading pigment into the forming fibre, and a hair is emerging at a steady rate.

On the scalp, anagen lasts roughly two to six years — some follicles longer, up to about seven. This is the phase that dominates: on a healthy adult scalp, somewhere around 85–90% of follicles are in anagen at any moment (Kligman, 1959; Headington, 1984; Paus & Cotsarelis, 1999).

Catagen — the regression phase

Catagen is short and brutal: about two to three weeks. The lower two-thirds of the follicle regresses through a controlled programme of apoptosis. The matrix stops dividing, pigment production shuts down, and the follicle draws upward toward the skin surface, dragging the dermal papilla with it (Stenn & Paus, 2001).

Because catagen is so brief, it is rare in a snapshot: under 1% of scalp follicles on a normal biopsy.

Telogen — the resting phase

Telogen lasts approximately three months — commonly cited as around 100 days. The follicle is quiet. The old hair, now a club hair with a characteristic bulbous, unpigmented root, sits anchored in the shortened follicle. The dermal papilla rests beneath the bulge stem-cell reservoir, waiting.

On a normal scalp, roughly 10–15% of follicles are in telogen (Headington, 1984). With around 100,000 scalp follicles, that arithmetic is where the familiar 50 to 100 hairs a day figure comes from — it is not a rule someone invented, it is a consequence of the phase proportions and the cycle length.

The word resting has done real damage, incidentally. Telogen is not an idle state; it is an actively maintained one, held in place by inhibitory signalling that must be lifted before the next cycle can begin. The review literature has argued explicitly for redefining telogen as a maintenance stage rather than a dormant one (Geyfman et al., 2015).

Exogen — the release phase

The fourth phase most consumer articles skip. Exogen is the active shedding of the club hair — a distinct, regulated release event rather than a passive falling-out, and it does not necessarily coincide with the start of the next anagen. A follicle can hold its club hair while the new one is already growing beneath it, which is why you sometimes shed a hair and see no gap.

Naming exogen matters practically: it means shedding and cycling are semi-independent. A change in shedding rate is not automatically a change in growth.

Why Scalp Hair Grows to Your Waist and Eyebrows Do Not

This is the question that makes the whole system click, and almost nobody asks it.

Your eyebrow hairs and your scalp hairs grow at broadly similar rates. Neither is a faster-growing hair in any meaningful sense. So why is one a centimetre long and the other three feet?

Because terminal length is growth rate multiplied by anagen duration — and anagen duration is set by the follicle, not by the hair.

• Scalp anagen: years. At roughly 1 cm per month over, say, five years, that is about 60 cm of hair. Longer anagen, longer hair.
• Eyebrow anagen: weeks. Eyebrow follicles run a growth phase measured in weeks rather than years, with a correspondingly larger proportion of follicles in telogen at any moment (Nguyen et al., 2014). The hair reaches its length, stops, and is replaced.

Nothing cuts your eyebrows. Their follicles simply run a much shorter programme, and that programme length is a property of the dermal papilla in each follicle — the same cells that set fibre calibre. Regional identity in the follicle is remarkably stable: this is why eyebrow hairs transplanted to the scalp continue behaving like eyebrow hairs for a considerable time.

Two consequences follow, and both come up constantly in clinic.

One: your maximum hair length is largely inherited. If your hair never grows past your shoulders, that is usually not damage or breakage — it is a genetically shorter anagen. You can protect the ends and avoid losing length to breakage, but you cannot extend anagen with a conditioner.

Two: shortened anagen is precisely what androgen-driven hair loss does. Pattern hair loss progressively shortens the growth phase, cycle by cycle, so each successive hair is shorter and finer before it is released (Whiting, 2001). The eyebrow comparison is not a curiosity. It is a preview of the mechanism.

Asynchronous Cycling: Why You Do Not Moult

A dog sheds its coat. A deer changes coat twice a year. Their follicles cycle in waves — large fields of follicles moving through the phases together.

Human scalp follicles cycle asynchronously, in a mosaic. Your neighbouring follicles are at randomly different points in their programmes: one in year three of anagen, the next in week two of catagen, the next in month one of telogen. The pattern is scattered rather than patterned.

This is one of the more consequential facts about human hair and it is almost never stated:

• It is why you do not go bald every autumn. With around 10–15% of follicles resting and staggered, losses are spread thinly and invisibly across the whole scalp.
• It is why a hundred hairs a day is normal. Distributed across 100,000 follicles in mosaic, a hundred released hairs is a rounding error in density.
• It is why telogen effluvium looks alarming. A systemic stressor — high fever, surgery, a crash diet, childbirth, a severe illness — can push an abnormally large number of follicles into telogen at approximately the same time. That is a forced synchronisation, and it converts an invisible process into a visible one (Headington, 1993; Malkud, 2015).
• It is why the shedding stops on its own. Once the synchronised cohort has released, the mosaic re-scatters. Most acute telogen effluvium is self-limiting for exactly this reason.

Humans do retain a faint seasonal signal — measurable studies have found modest seasonal variation in the proportion of follicles in telogen, with a documented late-summer peak in some populations (Randall & Ebling, 1991). It is a statistical ripple on top of the mosaic, not a moult. If you shed slightly more in September, you are not imagining it and you are also not losing your hair.

The Numbers Worth Memorising

On growth rate: 1 cm a month is an average, not a law. Measured growth parameters differ meaningfully between individuals and between hair types — studies of hair growth profiles across populations document real variation in growth rate, anagen duration and density (Loussouarn, 2001; Loussouarn et al., 2005). And ageing shortens things: anagen duration declines with age, which is part of why hair that once reached the middle of your back no longer does (Courtois et al., 1995).

Follicle count is fixed. You were born with all the hair follicles you will ever have. Nothing on the market creates new ones. Every honest intervention in this category works on the follicles you still have — which is why the follicles you still have are the asset, and why timing matters so much.

The Three-Month Lag, and the Arithmetic It Forces

Now put the pieces together, because this is the section that changes how you interpret everything.

A follicle that is pushed out of anagen today does not shed today. It enters catagen for two to three weeks, then telogen for about three months, and only then releases its club hair.

So the shedding you see is reporting on an event roughly three months in the past.

This is why:

• Postpartum shedding peaks at around three months after delivery, not at delivery.
• Hair falls out about three months after a high fever, a surgery, or a hospital admission — by which time most people have stopped connecting the two (Headington, 1993).
• Crash dieting produces shedding in the spring for a January diet.
• The shedding continues for weeks after the cause has been fixed. The cohort already committed to telogen will complete its telogen regardless. Correcting a ferritin level today does not stop hairs that entered telogen in May from being released in August.

Run the arithmetic forward and you get the assessment window.

Suppose an intervention starts working immediately and perfectly — an unrealistically generous assumption. What has to happen before you can see it?

1. Follicles in telogen must be released and re-enter anagen. Depending where they sat in their ~100-day telogen when you started, that alone can take up to three months.
2. A new anagen hair must then grow from the bulb up through the follicle and emerge at the skin surface. That is several weeks before anything is visible.
3. It must then reach a length at which it contributes to what you perceive as density — perhaps 1–2 cm, which at 1 cm a month is another one to two months.

Add it up: the earliest point at which a genuine change in density can begin to be visible is around three months, and a fair assessment is closer to six. Nothing about that is a marketing position. It is the cycle's own arithmetic, and it applies identically to a prescription drug, a laser device, a supplement and a placebo.

This is the origin of the 90-day rule we apply across this site: do not judge anything before day 90, and do not conclude anything final before month six. Take standardised photographs in the same light at the same angle on day 0, day 90 and day 180, because your memory of your own scalp is not a measuring instrument.

A related point of honesty: some things can change inside 30 days, and confusing them with density is the trap. Fibre condition, shine, manageability, static, tangling, scalp comfort and flaking are surface and scalp-environment properties, and they can shift within weeks because they do not depend on the cycle. Density cannot. Density is a cycle-length problem, and cycles do not accelerate to suit anyone's marketing calendar.

What Can and Cannot Be Influenced

If a product's mechanism story does not eventually make contact with anagen duration or the anagen/telogen ratio, it is not addressed to hair loss. It may be an excellent haircare product. That is a different claim.

The Bottom Line

Every scalp follicle cycles independently through anagen (growth, ~2–6 years, 85–90% of follicles), catagen (regression, ~2–3 weeks, under 1%), telogen (maintenance, ~3 months, 10–15%) and exogen (release). Terminal hair length is growth rate — about 1 cm a month — multiplied by anagen duration, which is why scalp hair reaches your waist and eyebrow hair, whose anagen runs in weeks, does not (Nguyen et al., 2014). Human follicles cycle asynchronously in a mosaic rather than in waves, which is why you shed 50–100 hairs a day invisibly and why a systemic stressor that synchronises a cohort produces the sudden, frightening, and usually self-limiting shed of telogen effluvium (Headington, 1993; Malkud, 2015). Because telogen runs about three months, shedding reports on an event roughly three months old — the single most useful fact in this article. And because a released follicle must re-enter anagen, grow up through the follicle, and reach visible length, no intervention of any kind can demonstrate a change in density in less than about 90 days, with six months the fair assessment point. That arithmetic is the cycle's, not the marketing department's, and it applies equally to drugs, devices, supplements and placebo.

Dr. Susan Lin's Clinical Perspective

"I have watched patients make two mistakes with this cycle, in opposite directions. The first is panic — counting hairs in the drain in week two of a shed that will run its course by week twelve, and abandoning something reasonable because it has not worked yet. The second is the mirror image: staying on something for three years without ever establishing a baseline, and so never knowing whether anything changed. Both come from the same missing idea, which is that hair reports late. So I ask for three unglamorous things: a photograph on day zero, in daylight, at a fixed angle. A second at day ninety. A third at month six. Do that, and the cycle stops being a source of anxiety and becomes an instrument. Skip it, and you are asking memory to detect a change of a few percent. Memory is not that good."

— Dr. Susan F. Lin, M.D., Physician Formulator, MD HAIR

Mechanism Spotlight: The Club Hair, and How to Read a Shed Hair's Root

You can extract real information from a shed hair, and it takes about five seconds.

Look at the end that was in your scalp. If it carries a small, pale, bulbous, keratinised club — a rounded knob — that is a telogen club hair, and it left on schedule. This is the root morphology characteristic of the resting-phase hair, formed as the follicle regressed in catagen and anchored the old fibre in place (Stenn & Paus, 2001).

If instead the root is a soft, pigmented, tapered bulb, sometimes with a sheath attached, that hair was pulled out of anagen — it was still growing. A handful after aggressive brushing is mechanical. A consistent majority is not a normal shed pattern, and warrants a physician's assessment rather than a shopping decision.

If the hair broke along its length — no root, two frayed ends — that is breakage, not shedding. They are different problems with different solutions, and this test distinguishes them faster than any product claim will.

Structured versions of the same observation are how the cycle is measured clinically: the trichogram classifies plucked roots by phase, and horizontal scalp biopsy sections allow anagen-to-telogen and terminal-to-vellus ratios to be counted directly (Headington, 1984; Whiting, 1993). You are doing a crude version of a real diagnostic method.

Recommended Reading

Pillar pages on mdhair.com:

• Drug-Free Hair Loss Treatment — The Complete Guide — the pillar this article sits under
• The Scalp Health Guide
• The Clinical Evidence Behind MD HAIR
• The Lilac & Verbascoside Science

Related articles in this series:

• How Long Does It Take to Regrow Hair? A Realistic Timeline — the 90-day arithmetic above, applied month by month to what you will actually see
• Telogen Effluvium or Pattern Hair Loss? — the three-month lag in its most common clinical form, and how to tell the two conditions apart
• Postpartum Hair Loss: Why Your Hair Is Falling Out After Baby — the clearest example of synchronised cycling and spontaneous recovery
• Dermal Papilla Cells: The Cells That Decide Your Hair's Future — the cells that set anagen duration, and where the androgen story lands

Our sister site md-factor.com carries the full MD® line and long-form customer reviews, which are worth reading precisely because the useful ones describe months rather than days.

MD HAIR Product Recommendation

MD HAIR Restoration Kit — /products/hair-restoration-kit

Why this recommendation follows from this article, specifically. Everything above says the same thing in different ways: this is a cycle-length problem, and cycle-length problems are answered by consistency over months, not by intensity over days. The kit exists for that reason — it is the routine assembled so that daily application is one decision instead of four, over the 90 to 180 days that the arithmetic in this article demands. The most common reason a reasonable regimen fails is not that it was the wrong regimen. It is that it was abandoned in week five, during a shed that was reporting on events from before it started.

What I am not claiming. No product creates follicles, accelerates the growth rate of a hair fibre, or shortens the ~100-day telogen. The evidence for our topical system is a 119-day (17-week) study conducted by an independent third-party testing organisation, n = 24, on the two-step system rather than either product alone, self-reported, with no placebo arm. It was a split-scalp design — each participant serving as their own control, which is a genuine methodological strength and I will defend it. The report's own sentence, from the same document, is: "The satisfaction rate (concerning the overall efficacy) is not significantly validated." You should have that line at the same time as any percentage, which is why I have not quoted one without it.

Photograph day zero before you open anything. It costs nothing and it is the only way this article's arithmetic becomes usable to you.

If you do not yet know what is driving your shedding — and after a fever, a surgery, a birth or a large weight change, the answer is often not pattern hair loss at all — start with the MD HAIR Quiz rather than a product. Several of its outcomes route you to a physician and a laboratory panel, which is the correct answer more often than a purchase is.

A note on authenticity: genuine MD HAIR™ and MD Nutri Hair™ products are sold only through mdhair.com, md-factor.com, and the official La Cañada Ventures, Inc. stores on Amazon and Walmart.

References

1. Paus R, Cotsarelis G. (1999). The biology of hair follicles. New England Journal of Medicine, 341(7), 491–497. PMID 10441606
2. Stenn KS, Paus R. (2001). Controls of hair follicle cycling. Physiological Reviews, 81(1), 449–494. PMID 11152763
3. Kligman AM. (1959). The human hair cycle. Journal of Investigative Dermatology, 33, 307–316. PMID 14409844
4. Saitoh M, Uzuka M, Sakamoto M. (1970). Human hair cycle. Journal of Investigative Dermatology, 54(1), 65–81. PMID 5416680
5. Headington JT. (1984). Transverse microscopic anatomy of the human scalp: a basis for a morphometric approach to disorders of the hair follicle. Archives of Dermatology, 120(4), 449–456. PMID 6703750
6. Headington JT. (1993). Telogen effluvium: new concepts and review. Archives of Dermatology, 129(3), 356–363. PMID 8447677
7. Malkud S. (2015). Telogen effluvium: a review. Journal of Clinical and Diagnostic Research, 9(9), WE01–WE03. PMID 26500992
8. Geyfman M, Plikus MV, Treffeisen E, Andersen B, Paus R. (2015). Resting no more: re-defining telogen, the maintenance stage of the hair growth cycle. Biological Reviews, 90(4), 1179–1196. PMID 25410793
9. Nguyen JV, Dolan CK, Wolverton SE. (2014). The biology, structure, and function of eyebrow hair. Journal of Drugs in Dermatology, 13(1 Suppl), s12–s16. PMID 24385126
10. Loussouarn G. (2001). African hair growth parameters. British Journal of Dermatology, 145(2), 294–297. PMID 11531795
11. Loussouarn G, El Rawadi C, Genain G. (2005). Diversity of hair growth profiles. International Journal of Dermatology, 44(Suppl 1), 6–9. PMID 16187948
12. Courtois M, Loussouarn G, Hourseau C, Grollier JF. (1995). Ageing and hair cycles. British Journal of Dermatology, 132(1), 86–93. PMID 7756156
13. Randall VA, Ebling FJ. (1991). Seasonal changes in human hair growth. British Journal of Dermatology, 124(2), 146–151. PMID 2003996
14. Whiting DA. (1993). Diagnostic and predictive value of horizontal sections of scalp biopsy specimens in male pattern androgenetic alopecia. Journal of the American Academy of Dermatology, 28(5 Pt 1), 755–763. PMID 8496421
15. Whiting DA. (2001). Possible mechanisms of miniaturization during androgenetic alopecia or pattern hair loss. Journal of the American Academy of Dermatology, 45(3 Suppl), S81–S86. PMID 11511857
16. Olsen EA, Messenger AG, Shapiro J, et al. (2005). Evaluation and treatment of male and female pattern hair loss. Journal of the American Academy of Dermatology, 52(2), 301–311. PMID 15692478
17. Spincontrol North America, 119-day (17-week) study of the MD® two-step topical system, n = 24, split-scalp design, self-reported outcomes, no placebo arm. Internal report, study on file.

Dr. Susan F. Lin, M.D. is the physician formulator behind MD HAIR and MD Nutri Hair™, product lines of La Cañada Ventures, Inc. — physician-formulated since 2008 under the MD® mark (U.S. Reg. No. 4,471,494). She trained at Boston University School of Medicine and is board-certified in Obstetrics & Gynecology and in Anti-Aging Medicine (A4M).

This article is for educational purposes and does not constitute medical advice. Sudden, patchy, painful or scarring hair loss, and shedding that persists beyond six months, should be evaluated by a physician rather than managed with cosmetics. Consult your own physician for personalized guidance.

MD® products are cosmetics and dietary supplements manufactured in FDA-registered, GMP-compliant facilities. "FDA-registered" describes the facility, never the product: no MD product is FDA approved, and no cosmetic or dietary supplement is. Individual results vary. MD Nutri Hair™ is a dietary supplement. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Because there are no clinical data in pregnant or breastfeeding women, we do not advocate using MD HAIR products during pregnancy or lactation.

Explore more in the Verbascoside & Lilac Science series at mdhair.com/pages/lilac-verbascoside-science