Hair Growth Cycle: Anagen, Catagen, Telogen Explained: Hair loss is often confusing because the results of treatment are never immediate. You might apply a topical solution for months before seeing any change, or experience a sudden shed that seems to appear out of nowhere. To understand why this happens, you must first understand the biology of the hair growth cycle. Hair does not grow continuously. Instead, each follicle on your scalp operates independently, cycling through specific phases of growth, transition, and rest. This comprehensive guide explains the three phases of the hair cycle—Anagen, Catagen, and Telogen—and how understanding them is the foundation for choosing the right hair treatment.
The Basics: Why Hair Cycles
Hair follicles are tiny organs that undergo perpetual regeneration. The cycle ensures that we do not shed all our hair at once, maintaining a consistent density on the scalp. At any given time, approximately 85% to 90% of your hairs are in the active growth phase, while the rest are in a resting or shedding phase. Disruptions to this delicate cycle, whether from stress, hormones, or nutritional deficiencies, are what manifest as visible hair loss.
Phase 1: Anagen - The Growth Phase
The Anagen phase is the active period where cells in the hair bulb divide rapidly, forming the hair shaft. This is the phase that determines the length of your hair.
Duration: The Anagen phase lasts between two to seven years for scalp hair. This duration is genetically determined and varies from person to person. For example, individuals with very long hair have a longer Anagen phase, while those who struggle to grow their hair past their shoulders typically have a shorter one.
Activity: During Anagen, the follicle is deeply anchored in the subcutaneous layer of the skin, and the hair is actively being pushed upward. The cells are metabolically very active, which is why they are susceptible to damage from chemotherapy or nutritional deficiency.
Impact on Hair Loss: Treatments like Minoxidil work primarily by prolonging the Anagen phase and coaxing follicles that have a short growth period to stay in this phase longer. When you see increased "peach fuzz" or baby hairs during treatment, it is often because miniaturized follicles are being stimulated to re-enter a productive Anagen phase.
Phase 2: Catagen - The Transition Phase
The Catagen phase is a brief, transitional stage that signals the end of active growth. It is often described as the "regression" phase.
Duration: This phase is very short, lasting only about one to two weeks.
Activity: During Catagen, the hair shaft detaches from the blood supply and stops growing. The outer root sheath shrinks and attaches to the root of the hair, forming a club-like structure known as a "club hair." The follicle itself prepares to enter a resting state.
Impact on Hair Loss: This phase is mostly invisible. Because it is so short, you do not typically notice hair fall during Catagen. It is a controlled and necessary step to allow the follicle to renew itself.
Phase 3: Telogen - The Resting and Shedding Phase
The Telogen phase is the final part of the cycle, encompassing both a resting period and the eventual shedding of the hair. This is the phase most people associate with hair loss.
Duration: Telogen lasts approximately three to four months.
Activity: The follicle is completely at rest. The club hair is fully formed and is simply sitting in the follicle, no longer growing. Eventually, a new Anagen hair begins to grow underneath it, pushing the old Telogen hair out. This is why you typically lose 50 to 100 hairs a day—it is simply the old hair being ejected to make way for the new.
Impact on Hair Loss: This is the critical phase for understanding shedding disorders.
Telogen Effluvium: When the Cycle Breaks
Telogen Effluvium is the medical term for temporary hair shedding caused by a disruption in the cycle. A significant trigger (such as severe stress, illness, childbirth, or rapid weight loss) can shock a large number of Anagen hairs into prematurely transitioning to Telogen.
Because the Telogen phase lasts 3 to 4 months, the shedding does not happen immediately after the trigger. This is the "delay" that confuses many people. For example, a high fever in January may result in noticeable handfuls of hair falling out in April. The body simply synchronized a massive batch of follicles to enter the resting phase simultaneously, leading to a diffuse shed 90 to 120 days later.
The Hair Cycle and Seasonal Shedding
The hair cycle is also influenced by environmental factors, leading to the phenomenon of seasonal shedding. Research indicates that more hairs enter the Telogen phase during the summer. This is believed to be an evolutionary mechanism to provide a thicker coat for UV protection. Consequently, the shedding of these Telogen hairs peaks in the late fall and early winter, which is why many people notice increased hair loss around October and November. A similar, often less pronounced, shedding occurs in the spring.
How Treatments Interact with the Hair Cycle
Understanding these phases explains why patience is required for any hair loss treatment.
The Shedding Phase on Minoxidil: When you start Minoxidil, you may experience an initial increase in shedding. This is a positive sign. The medication is rapidly pushing Telogen hairs out to make way for new, healthier Anagen growth.
Delayed Results: Because it takes months for a follicle to complete the Telogen phase and re-enter a productive Anagen phase, you cannot expect to see results from any treatment (whether topical, oral, or laser) in less than three to six months. The follicle must physically complete its cycle.
Targeting the Right Phase: Drugs like Finasteride work hormonally to protect the follicle during the Anagen phase, preventing DHT from shortening its lifespan. Therapies like PRP aim to inject growth factors directly into the scalp to stimulate follicles to exit Telogen and re-enter Anagen.
The Role of the Hair Bulb
The bulb is the living part of the hair located deep within the follicle. It contains the dermal papilla, which is rich with blood vessels and nerves that feed the hair. When you examine a hair that has fallen out, looking at the bulb can provide clues:
Club Hair (Telogen): If the root has a small, white, bulbous tip (a club), it is a naturally shed Telogen hair. This is normal.
Dystrophic Anagen Hair: If the root is absent or the shaft is broken, it may indicate damage to the follicle during the growth phase, sometimes caused by inflammation or aggressive chemical treatments.
Hair Growth Cycle
The hair growth cycle is a dynamic, continuous process. The Anagen phase dictates length, Catagen is the short transition, and Telogen is the resting and shedding period. Most common hair loss conditions, from telogen effluvium to androgenetic alopecia, are essentially disorders of this cycle—either too many hairs enter Telogen at once, or the Anagen phase becomes too short. By understanding these three phases, you gain the ability to set realistic expectations for treatment, understand the timing of shedding, and better interpret what your hair is telling you about your overall health.
Advanced FAQ on the Hair Growth Cycle
Q: Does the hair growth cycle change as we age?
A: Yes. As we age, particularly in cases of androgenetic alopecia, the Anagen phase progressively shortens. This results in hairs that are finer, shorter, and less pigmented (vellus hairs). The time between the shedding of a Telogen hair and the regrowth of a new Anagen hair may also lengthen, leading to visible thinning.
Q: Can you actually feel the different phases of the hair cycle?
A: No. The biological processes of the hair cycle occur deep within the follicle beneath the scalp's surface. There are no nerve endings that signal whether a hair is in Anagen, Catagen, or Telogen. You only notice the result when the hair is shed or when regrowth appears.
Q: How long does it take for a hair to grow from the bulb to the surface?
A: Once a hair is formed in the bulb during the Anagen phase, it must traverse the follicle canal and the epidermis. This process takes approximately two weeks from the moment of formation to the point where the hair shaft emerges above the scalp's surface.
Q: Does shaving or cutting hair affect the growth cycle of the follicle?
A: No. Shaving, trimming, or cutting the hair shaft has absolutely no effect on the living follicle beneath the scalp. The hair cycle is regulated internally by hormones, genetics, and blood flow. The myth that shaving makes hair grow back thicker is an optical illusion caused by the blunt tip of the cut hair.
Q: Can certain medications extend the Anagen phase artificially?
A: Yes. This is precisely how Minoxidil works. It prolongs the duration of the Anagen phase and can also convert resting (Telogen) follicles back into active (Anagen) follicles. This is why consistent, long-term use is required—once the medication is stopped, the follicles revert to their genetically programmed short Anagen cycle.
Q: Why does pregnancy often make hair look thicker?
A: During pregnancy, high levels of estrogen prolong the Anagen phase and significantly delay the onset of the Telogen phase. Fewer hairs enter the resting and shedding phase, leading to a buildup of hair and a perceived increase in density. This is followed by the dramatic postpartum shed (Telogen Effluvium) when hormone levels drop and the delayed shedding finally occurs.
Q: Is the hair cycle on other parts of the body the same as on the scalp?
A: The phases are the same (Anagen, Catagen, Telogen), but the duration of the Anagen phase is dramatically different. For example, the Anagen phase for eyebrow hair is only a few weeks, which is why they never grow as long as scalp hair. Scalp hair has the longest Anagen phase of any hair on the human body.
Q: Can extreme dieting or fasting interrupt the hair cycle?
A: Yes. Severe caloric restriction or rapid weight loss is a classic trigger for Telogen Effluvium. The body perceives the lack of nutrients as a stressor and diverts energy away from non-essential functions like hair growth, pushing follicles into the resting phase.
Q: What is the "kenogen" phase?
A: Kenogen is a term used to describe an "empty" follicular state. It is the lag period between the shedding of a Telogen hair and the emergence of a new Anagen hair. In healthy follicles, this period is short. In androgenetic alopecia, this lag phase becomes longer, and the follicle remains empty for extended periods, contributing to the appearance of baldness.
Q: Do hair growth cycles synchronize after a major event?
A: Yes. A major physiological stress (like high fever, surgery, or childbirth) can force a large percentage of Anagen hairs to synchronously enter Catagen and then Telogen. This leads to the "wave" of shedding seen in Telogen Effluvium, where all the affected hairs fall out around the same time, 3 to 4 months after the trigger.
Article Last Reviewed: March 2026