The Hair Growth Cycle
Anagen, Catagen, Telogen & Exogen
Understand how hair grows, rests, sheds, and renews—and what changes in that rhythm can mean for your hair.
Every follicle follows its own rhythm.
The hair growth cycle is the repeating process through which each follicle produces, maintains, releases and replaces a hair.
Scalp follicles do not all move through the cycle at the same time. Most are actively growing hair, while smaller proportions are transitioning, resting or releasing an existing hair shaft.
This staggered activity helps maintain relatively stable scalp coverage. However, illness, hormonal changes, medication, rapid weight loss, nutritional deficiency, inflammation and genetic hair loss can alter the balance between the phases.
This guide explains the four commonly recognized stages of the hair growth cycle: anagen, catagen, telogen and exogen. It also explains how cycle disruption can lead to shedding, thinning or reduced hair length.
Key Takeaways
- Hair grows in repeating cycles. The principal phases are anagen, catagen and telogen, followed by the shedding process known as exogen.
- Anagen is the active growth phase. Approximately 80–90% of healthy scalp hairs are usually in anagen.
- Catagen is a short regression phase. Active shaft production stops while the lower follicle undergoes controlled structural change.
- Telogen is the resting phase. The club hair remains within the follicle before being released.
- Exogen describes shedding. It is the process through which the retained club hair is released from the follicle.
- Each follicle cycles independently. This prevents all scalp hair from growing and shedding simultaneously.
- Cycle disruption can produce hair loss. Telogen effluvium, anagen effluvium and androgenetic alopecia affect the cycle in different ways.
- Hair products cannot control every part of the cycle. Diagnosis matters because genetic, hormonal, immune and medical causes require different management.
Hair Follicle and Hair Shaft Anatomy
Hair has two broad components: the follicle below the skin and the visible shaft that emerges from it.
The Hair Follicle
The hair follicle is a complex mini-organ embedded in the skin. It repeatedly remodels itself as it passes through growth, regression and rest.
Important follicular structures include:
- Hair bulb: the enlarged lower portion of an actively growing follicle.
- Hair matrix: rapidly dividing cells that help form the developing hair shaft and inner root sheath.
- Dermal papilla: a specialized group of mesenchymal cells that exchanges growth-regulating signals with the surrounding follicular cells.
- Melanocytes: pigment-producing cells that provide melanin to the growing hair during anagen.
- Outer root sheath: a follicular structure continuous with the epidermis and containing important cell populations.
- Bulge region: an area containing epithelial stem cells involved in follicular regeneration.
Blood vessels surrounding the lower follicle support the metabolically active tissues during growth. However, the visible hair shaft itself does not contain blood vessels or nerves.
The Hair Shaft
The visible hair shaft consists mainly of nonliving, keratinized cells. Its principal layers are:
- Cuticle: the overlapping outer protective layer.
- Cortex: the main structural layer that provides much of the hair’s strength, elasticity and color.
- Medulla: a central region that may be present, fragmented or absent depending on the hair.
Because the visible shaft is not living tissue, damaged lengths cannot biologically heal. Conditioners and treatments may temporarily coat, smooth or reinforce the shaft, but they do not restore it to an undamaged state.
Learn more about keratin and hair structure.
How Does the Hair Growth Cycle Work?
Human scalp hair is commonly described as moving through four stages:
- Anagen: active growth
- Catagen: regression or transition
- Telogen: rest
- Exogen: release or shedding
These phases are not synchronized across the scalp. Each follicle follows its own biological timetable.
| Phase | What Happens | Typical Scalp Duration | Approximate Proportion |
|---|---|---|---|
| Anagen | The follicle actively produces a pigmented hair shaft. | Usually several years | Approximately 80–90% |
| Catagen | Active growth stops and the lower follicle undergoes controlled regression. | Approximately 2–3 weeks | Approximately 1–3% |
| Telogen | The follicle rests while the club hair remains retained. | Approximately 3–4 months | Approximately 10–15% |
| Exogen | The retained club hair is released and shed. | Variable and overlapping | Not usually expressed as a separate fixed percentage |
These figures are useful estimates rather than universal measurements. The proportions and durations vary by person, body site, age, health, hormones and measurement method.
Anagen: The Active Growth Phase
Anagen is the longest phase of the scalp hair cycle. During this period, matrix cells in the lower follicle divide rapidly and contribute to production of the hair shaft.
Melanocytes provide pigment to the developing hair. Meanwhile, the follicle remains deeply extended within the skin and maintains active signaling between its epithelial and dermal components.
Approximately 80–90% of healthy scalp follicles are typically in anagen at a given time.
How Long Does Anagen Last?
Scalp anagen generally lasts several years. Estimates commonly range from approximately two to six years, although shorter and longer cycles occur.
The length of anagen helps determine the maximum length a hair can reach before it stops growing. A person with a longer anagen phase can generally grow longer scalp hair than someone with a naturally shorter phase, assuming the shaft does not break.
Body hair, eyebrows and eyelashes have much shorter growth phases. This is one reason they do not normally reach the same length as scalp hair.
How Fast Does Scalp Hair Grow?
Scalp hair grows at an average rate of approximately one centimeter per month. This varies between individuals and even between different follicles on the same scalp.
Trimming the ends does not make follicles grow faster. However, removing split or damaged ends may reduce further breakage and help the retained hair look healthier.
What Influences Anagen?
Factors that may influence the duration or activity of anagen include:
- Genetics
- Age
- Androgen sensitivity
- Thyroid and other hormonal conditions
- General health
- Severe illness
- Energy and protein availability
- Documented nutrient deficiency
- Medication
- Inflammatory or autoimmune disease
No shampoo or cosmetic ingredient can guarantee that a follicle will remain in anagen for a specific number of years.
Catagen: The Regression Phase
Catagen is a short, highly regulated phase that follows anagen.
During catagen:
- Active hair-shaft production stops.
- Cell division in the matrix declines.
- Pigment production stops.
- The lower portion of the follicle regresses.
- The follicle becomes shorter.
- The proximal hair is transformed into a club hair.
The dermal papilla and epithelial components change their relationship during this regression. However, the permanent upper follicle remains in place and can contribute to the next cycle.
Catagen usually lasts approximately two to three weeks, and only a small proportion of scalp follicles are in this phase at one time.
Telogen: The Resting Phase
Telogen is the relatively inactive or resting stage that follows catagen.
The fully keratinized club hair remains retained within the upper follicle during this period. The follicle is not producing a lengthening hair shaft, but it is not biologically dead.
Telogen commonly lasts around three to four months on the scalp. Approximately 10–15% of scalp hairs may normally be in telogen, although estimates vary.
Signals that initiate the next anagen phase reactivate follicular growth. The new growing hair and the shedding system eventually contribute to release of the older club hair.
Exogen: The Shedding Phase
Exogen describes the active release of the club hair from the follicle.
Shedding may occur during washing, brushing, styling or ordinary daily activity. The hair that falls has already stopped growing and has been retained for a period before release.
Exogen can overlap with telogen and with the beginning of a new anagen phase. Therefore, it should not be described simply as a completely separate “new hair” phase.
How Much Daily Shedding Is Normal?
Approximately 50–100 shed scalp hairs per day is commonly used as a general reference range. However, counting daily hairs is imprecise.
The amount noticed on a particular day depends on:
- How often the hair is washed
- Brushing and styling habits
- Total hair density
- Hair length and curl pattern
- Whether shed hairs remain trapped within surrounding hair
- Protective styles, braids or extensions
Someone who washes once a week may see several days of retained shed hairs released together. That does not automatically mean the follicles shed all those hairs on the same day.
What Is Kenogen?
Kenogen is a term used for an interval in which a follicle is empty after the previous hair has been shed and before a new shaft emerges.
It is not always included in simplified descriptions of the cycle. A prolonged empty-follicle interval may contribute to reduced visible density in some hair-loss conditions.
Kenogen should not be confused with exogen:
- Exogen: release of the existing club hair.
- Kenogen: an empty-follicle interval before a replacement hair emerges.
How the Hair Cycle Changes Across the Body
Follicles in different body areas follow different biological schedules.
Scalp follicles have a long anagen phase, allowing the hair to grow for years. Eyebrow, eyelash and body-hair follicles spend much less time in active growth. Therefore, their hairs reach a shorter natural length.
The difference is mainly determined by follicle programming, not by cutting or shaving. Shaving does not change the follicle’s cycle, number or growth rate.
How Hair-Loss Conditions Disrupt the Cycle
Shedding and thinning can reflect very different changes within the follicle.
- 1
Telogen Effluvium
Telogen effluvium occurs when an increased number of follicles transition from anagen into telogen.
Because telogen hairs remain retained before shedding, the increase in hair fall is usually delayed. It commonly becomes noticeable approximately two to four months after the trigger.
Possible triggers include:
- Febrile illness or severe infection
- Major surgery
- Childbirth
- Rapid weight loss
- Restrictive eating or inadequate protein intake
- Iron deficiency or another relevant deficiency
- Thyroid disease
- Selected medications
- Severe physiological stress
Telogen effluvium usually causes diffuse shedding rather than smooth, completely bald patches.
- 2
Anagen Effluvium
Anagen effluvium results from disruption of actively dividing cells within anagen follicles.
It is most strongly associated with cytotoxic chemotherapy. Hair loss can begin within days or weeks because the growing shaft becomes narrowed, weakened or abruptly disrupted.
Read more about hair regrowth after chemotherapy.
- 3
Androgenetic Alopecia
In androgenetic alopecia, susceptible follicles gradually miniaturize.
Over repeated cycles:
- Anagen becomes shorter.
- The produced hair becomes finer and shorter.
- The interval before replacement may increase.
- Visible scalp coverage progressively declines.
This is different from a single temporary shedding episode, although androgenetic alopecia and telogen effluvium can occur together.
- 4
Alopecia Areata
Alopecia areata is an immune-mediated condition that disrupts active follicles. It commonly causes smooth patches of nonscarring hair loss, although diffuse and extensive forms also occur.
The follicles are not necessarily destroyed, which means regrowth is possible. However, the course is unpredictable and requires condition-specific medical assessment.
- 5
Scarring Alopecia
Scarring alopecias involve inflammatory damage to follicular structures. Once a follicle is permanently destroyed and replaced by scar tissue, it cannot restart a normal hair cycle.
Burning, pain, pustules, redness, heavy scale or loss of visible follicular openings requires prompt dermatologic assessment.
Can You Restart or Extend the Hair Growth Cycle?
No single treatment works for every type of cycle disruption.
Treatment depends on the diagnosis:
- Correcting a confirmed deficiency may help when that deficiency is contributing to shedding.
- Treating thyroid disease may restore a more normal cycle when thyroid dysfunction is responsible.
- Addressing illness, rapid weight loss or inadequate intake may allow telogen effluvium to recover.
- Minoxidil may support anagen activity in selected hair-loss conditions.
- Antiandrogen treatment may help appropriate patients with androgenetic alopecia.
- Immune-directed treatment may be required for alopecia areata.
- Anti-inflammatory treatment is essential in active scarring alopecia.
Products advertised as “follicle stimulants” should not be assumed to change the human hair cycle without suitable clinical evidence.
Do Supplements Improve the Hair Growth Cycle?
Nutrients are necessary for normal follicular activity. However, that does not mean more supplementation creates faster growth.
Supplements are most relevant when there is:
- A confirmed deficiency
- Inadequate dietary intake
- Malabsorption
- A medically identified increased requirement
Excessive vitamin A, selenium and certain other nutrients can contribute to hair loss. High-dose supplementation should therefore not be used as a substitute for assessment.
Learn more about nutritional deficiencies and hair loss.
How to Track Shedding and Regrowth
Daily counting is often unreliable and can increase anxiety. A more useful approach includes:
- Standardized scalp photographs every four weeks
- The same lighting, hairstyle, part and camera distance
- Recording the date shedding began
- Documenting illness, surgery, weight loss, medication and hormonal changes
- Noting scalp symptoms such as pain, itching, scale or burning
- Professional trichoscopy when available
Visible density changes slowly. Even after shedding improves, recovering length and volume can take many months.
When to Get the Hair Cycle Assessed
Arrange a professional assessment when:
- Heavy shedding continues for more than several months
- The central part or crown is progressively widening
- The hairline is receding
- Smooth bald patches appear
- Eyebrows or eyelashes are also affected
- The scalp is painful, burning, red or heavily scaled
- Pustules or crusting develop
- Follicular openings appear to be disappearing
- Hair loss begins after a medication change
- Shedding follows rapid or unexplained weight loss
A trichologist can document the pattern and scalp findings. A dermatologist or other appropriately qualified healthcare professional is required when medical diagnosis, laboratory investigation, prescription treatment or biopsy may be needed.
Frequently Asked Questions
What are the four stages of the hair growth cycle?
The four commonly described stages are anagen, catagen, telogen and exogen. Some scientific models also describe kenogen, an interval when a follicle remains empty before a replacement hair emerges.
How long is the hair growth cycle?
A complete scalp cycle commonly takes several years because anagen alone can last approximately two to six years or longer. Catagen lasts weeks, while telogen generally lasts several months.
Which phase makes hair grow?
Anagen is the active growth phase. Matrix cells in the lower follicle contribute to production of the hair shaft during this period.
Which phase causes hair shedding?
The club hair is retained during telogen and released during exogen. Excessive shedding may occur when an unusually large number of follicles move into telogen after a trigger.
How much hair shedding is normal?
Approximately 50–100 scalp hairs per day is a commonly used estimate. However, the amount seen on any one day depends on washing, brushing, hair density, texture and styling practices.
Does cutting hair restart the growth cycle?
No. Cutting changes only the visible shaft. It does not alter the biological activity of the follicle below the skin.
Does shaving make hair grow back thicker?
No. Shaving creates a blunt hair tip that may feel coarser as it emerges, but it does not increase follicle number, shaft diameter or growth rate.
Can shampoo keep hair in the anagen phase?
Ordinary shampoo cleans the scalp and hair. It should not be expected to extend anagen or treat genetic, hormonal or autoimmune hair loss unless it contains a specifically studied active ingredient used for an appropriate condition.
Can stress interrupt the hair cycle?
Significant physiological stress can trigger telogen effluvium. The shedding commonly appears several months after the triggering event rather than immediately.
How long does regrowth take after telogen effluvium?
Shedding may gradually settle over several months once the trigger has resolved. Restoring visible length and density takes longer because new scalp hair grows only about one centimeter per month on average.
Understand the Pattern Before Choosing Treatment
A disrupted hair cycle can produce diffuse shedding, progressive miniaturization or rapid loss of growing hairs. Identifying which pattern is present is more useful than trying random growth products.
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See what a hair assessment includes →Conclusion
The hair growth cycle is a continuous process of growth, regression, rest and release.
Most scalp follicles are normally in anagen, while smaller proportions are in catagen and telogen. Exogen releases the old club hair, and the follicle continues into another cycle.
Temporary or progressive hair loss can occur when this balance changes. The correct response depends on whether the problem is telogen shedding, disruption of growing hairs, progressive miniaturization, immune activity or inflammatory follicular damage.
Understanding the cycle provides useful context, but the visible pattern and underlying cause still determine the right investigation and treatment.
References
- Natarelli N, et al. Integrative and Mechanistic Approach to the Hair Growth Cycle and Hair Loss.
- Schneider MR, Schmidt-Ullrich R, Paus R. The Hair Follicle as a Dynamic Mini-Organ.
- Harkey MR. Anatomy and Physiology of Hair.
- Oh JW, et al. A Guide to Studying Human Hair Follicle Cycling In Vivo.
- DermNet. Telogen Effluvium.
- Hughes EC, Syed HA, Saleh D. Telogen Effluvium. StatPearls.
- Asghar F, et al. Telogen Effluvium: A Review of the Literature.
- Gupta S, et al. Anagen Effluvium: A Trichoscopic Analysis.
- Headington JT. Telogen Effluvium: New Concepts and Review.
- Yin GOC, et al. Telogen Effluvium: A Review of the Science and Current Obstacles.
Medical disclaimer: This article is provided for general educational purposes and does not replace diagnosis or individualized medical advice. Sudden, persistent, patchy, painful or inflammatory hair loss should be assessed by an appropriately qualified professional.