The Hair Growth Cycle Explained: Anagen, Catagen, Telogen

Understanding the hair growth cycle, the repeating sequence every hair follicle goes through, helps explain why hair loss is not always a cause for alarm, why some hair loss patterns signal a real problem, and why hair growth treatments take months to show results. This guide breaks down each phase of the cycle and what can disrupt normal hair growth patterns.

Overview of the Hair Growth Cycle

Every hair follicle on your scalp cycles independently through four phases: anagen (active growth), catagen (transition), telogen (resting), and exogen (shedding). Because follicles are not synchronized, some are always in each phase at any given time, which is why healthy scalps shed some hair every single day without ever going bald. Understanding this cycle is fundamental to understanding both normal hair shedding and the various forms of hair loss that occur when the cycle is disrupted.

Anagen Phase: Active Growth

The anagen phase is the active growth period, during which hair follicles are actively producing new hair cells, causing the strand to lengthen. This is the longest phase of the cycle, typically lasting two to seven years, and its duration largely determines your maximum potential hair length, since hair stops growing once a follicle exits this phase. At any given time, approximately 85-90% of scalp hair is in the anagen phase.

Catagen Phase: Transition

The catagen phase is a brief transitional period, lasting about two to three weeks, during which the hair follicle shrinks and detaches from its blood supply, effectively signaling the end of active growth for that particular strand. Only a small percentage of hair, roughly 1-3%, is in this phase at any given time.

Telogen Phase: Resting

During the telogen phase, the hair follicle is dormant, neither growing nor actively shedding, typically lasting around three months. About 10-15% of scalp hair is in this phase at any given time under normal, healthy conditions. At the end of telogen, the follicle will either begin a new anagen phase (pushing out the old hair) or move into the exogen phase.

Exogen Phase: Shedding

The exogen phase is when the resting hair is finally shed, either through daily activities like brushing and washing or as a new hair begins growing in the same follicle, pushing the old strand out. This phase can overlap with the beginning of a new anagen phase in the same follicle, which is part of why the transition from one hair to its replacement is often seamless and unnoticeable.

How Long Each Phase Lasts

Normal Daily Hair Shedding

Losing 50 to 100 hairs per day is considered within the normal range, reflecting the natural turnover of follicles moving through the telogen and exogen phases. This can vary somewhat by hair length and thickness, since longer, thicker hair may appear to shed more simply because each strand is more visible when it falls. Shedding that significantly exceeds this range, or that comes with visible thinning over time, may indicate a disruption to the normal cycle worth investigating.

What Disrupts the Hair Growth Cycle

• Telogen effluvium: a stress-related condition where a larger-than-normal percentage of hairs simultaneously shift into the telogen phase, leading to noticeable shedding roughly two to three months after the triggering event (illness, major stress, significant weight loss, childbirth)
• Androgenetic alopecia (pattern hair loss): progressively shortens the anagen phase over successive cycles, leading to shorter, finer hairs over time
• Nutritional deficiencies: particularly iron, protein, and certain vitamins, can shift the balance of the cycle toward more hairs in telogen
• Certain medications: some drugs can disrupt normal cycling as a side effect
• Thyroid conditions: both hyperthyroidism and hypothyroidism can affect the hair growth cycle

Our guide on causes of hair loss in women covers several of these disruptions in more depth.

Comparison Table: The Four Phases

Why Hair Growth Treatments Take Months to Work

Because the anagen (growth) phase can last years and the full cycle from growth to shedding spans months, hair growth treatments, whether topical minoxidil, supplements, or other interventions, require sustained use over at least three to six months before meaningful results become visible. This is because any newly stimulated growth still has to move through the normal phases of the cycle before becoming visibly longer or thicker, and existing hairs already in later phases of their cycle will not be affected by a treatment that primarily influences new growth initiation.

How the Hair Growth Cycle Changes With Age

The hair growth cycle is not entirely static throughout life, and understanding how it naturally shifts with age helps set realistic expectations about hair changes that are a normal part of aging rather than necessarily a sign of an underlying problem.

As people age, particularly from midlife onward, individual anagen phases tend to gradually shorten, meaning each hair spends somewhat less time in active growth before cycling into catagen and telogen. This shortening explains why maximum achievable hair length often decreases somewhat with age, even without any change in growth rate itself, since less total time in the growth phase means less total length achieved before a strand naturally sheds.

Follicle miniaturization, a separate but related age-related process, can also cause each successive hair produced by a given follicle to be slightly thinner and finer than the one before it, a gradual process that contributes to the overall thinning many people notice as they age, distinct from more dramatic pattern hair loss driven by genetics and hormones. This age-related miniaturization happens to some degree in nearly everyone, though its severity and visibility vary considerably based on genetic predisposition.

Hormonal changes associated with aging, including menopause and andropause, can also influence the balance of the cycle, sometimes pushing a higher percentage of hairs into the telogen phase or accelerating the miniaturization process described above, which is part of why hair changes often become more noticeable during these specific life transitions rather than gradually and evenly throughout adulthood.

Common Mistakes to Avoid

Panicking Over Normal Daily Shedding

Losing 50 to 100 hairs daily is a normal part of the hair growth cycle, not a sign of a problem, and does not necessarily warrant treatment or concern.

Expecting Immediate Results From Hair Growth Products

Given the multi-month duration of the growth cycle, expecting visible results within days or a couple of weeks from any hair growth treatment sets an unrealistic timeline.

Ignoring a Sudden, Significant Increase in Shedding

While daily shedding is normal, a noticeable, sustained increase, especially if it follows a stressful event, illness, or major life change, may indicate telogen effluvium and is worth investigating, even though it often resolves on its own over several months.

Assuming All Hair Loss Follows the Same Pattern

Different underlying causes, pattern hair loss, telogen effluvium, nutritional deficiencies, disrupt the cycle in different ways, meaning treatment approaches need to match the actual underlying cause.

How Different Body Areas Have Different Growth Cycles

While this guide has focused on scalp hair, it is worth noting that hair growth cycles vary considerably across different areas of the body, which explains several everyday observations people have about hair growth that might otherwise seem puzzling.

Eyelashes and eyebrows have a much shorter anagen phase than scalp hair, typically lasting only weeks rather than years, which is why these hairs never grow particularly long and why eyelash and eyebrow growth serums, when they work, tend to show more noticeable results within a shorter timeframe compared to scalp hair growth treatments. This shorter cycle also means eyelashes and eyebrows fully replace themselves much more frequently than scalp hair does.

Leg, arm, and other body hair similarly follows a much shorter growth cycle than scalp hair, which is part of why body hair rarely grows beyond a certain length even when left unshaved for extended periods, unlike scalp hair, which can grow for years and reach substantial length in people with a longer anagen phase.

This variation across body areas is a helpful, often overlooked point of context: the multi-month timeline associated with scalp hair growth treatments does not apply uniformly to every hair-growth-related product, since eyelash and eyebrow serums, for instance, are working with a fundamentally different, shorter cycle.