Hair Cycle – The 5 Phases

How Understanding Anagen, Telogen & Shedding Guides Effective Treatment

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Can understanding hair cycle improve hair transplant results?

Hair length is primarily a function of follicle programming, not just hair strength. The human scalp follicle is uniquely adapted for prolonged growth among mammals. Effective hair loss treatment requires working with your hair’s natural growth cycle, not against it.

The cycle’s five distinct phases determine how and when therapies can be successfully applied. Misapplied treatment during sensitive phases can be ineffective or even harmful, making this knowledge foundational to any clinical plan. Understanding these intrinsic cycles is essential in hair science, explaining everything from personal grooming to the diagnosis of hair growth disorders.

Sara’s Comment

The hair growth cycle—comprising the anagen (growth), catagen (transition), and telogen (resting) phases—varies dramatically across body regions in humans and differs even more between species. Crucially, the maximum length hair can reach is directly determined by the duration of its anagen phase: the longer the anagen, the longer the hair grows before shedding.

What are the 5 phases of the hair growth cycle?

The scalp hair cycle repeats approximately 20 times in a lifetime. Each follicle operates independently, progressing through these phases:

1. Anagen (Growing Phase)

This active growth period lasts 2-7 years. Hair follicles are deeply rooted in the dermis, producing long, pigmented hair. The goal of most treatments (like minoxidil or PRP) is to prolong this phase and stimulate more follicles to enter it.

2. Catagen (Transitional Phase)

A short, 2-3 week regression period. Growth stops, the hair follicle shrinks, and its base begins to detach from the blood supply. This is a preparatory phase for resting.

3. Telogen (Resting Phase)

A 3-4 month dormancy period where the hair is fully formed but not growing. At any time, roughly 10-15% of scalp hairs are in this phase. Excessive stress or shock can prematurely push more hairs into telogen, causing diffuse shedding (telogen effluvium).

4. Exogen (Shedding Phase)

An active shedding process where the telogen hair is released and falls out. This is a normal part of the cycle, with 50-100 shed hairs per day being typical. It makes way for the next growth cycle.

5. Kenogen (Empty Phase)

A recently defined phase where the follicle remains empty after the hair sheds and before a new anagen hair emerges. Prolonged kenogen may be a factor in pattern hair thinning.

The Hair Growth Cycle: Beyond Simple Growth & Shedding

The human hair growth cycle is a complex, multi-phase biological process, not a simple loop of growing and falling out. It consists of distinct, regulated phases—Anagen (growth), Catagen (transition), Telogen (rest), and Exogen (shedding)—that vary significantly across the body and throughout a person’s life.

Key, lesser-known facts about this cycle include:

Dramatic Duration Differences: A single scalp hair can grow actively (Anagen) for 2-7 years, while an eyebrow hair’s growth phase lasts only 4-6 weeks.
Independent Follicle Clocks: Each hair follicle operates on its own individual cycle timer. This asynchronous growth prevents mass shedding and creates the invisible mosaic of hair renewal on your scalp.
Acute Stress Response: Significant physiological or emotional stress can trigger Telogen Effluvium, abruptly pushing a large percentage of growing hairs into the resting/shedding phase, often manifesting as noticeable hair loss 2-3 months later.
Seasonal & Hormonal Influences: Studies suggest hair growth and shedding rates can fluctuate with seasons and are influenced by hormones, not just genetics.

Understanding this intricate cycle is fundamental to diagnosing hair loss. Distinguishing between a normal shedding phase (exogen) and a pathological disruption of the growth cycle (anagen or telogen effluvium) is a core principle of trichology and hair restoration medicine.

Human Hair Growth Cycle: Duration, Length & Biological Clocks

Hair growth is not uniform across the body. Each follicle type has a genetically programmed biological clock that dictates its Anagen (growth) phase duration, which directly determines its maximum possible length. This explains why scalp hair can grow very long, while eyebrows and body hair cannot.

Human Hair Cycle Variations by Body Site

Scalp Hair:

Anagen Duration: 2–7 years (average 3–5 years)
Average Maximum Length: 30–100 cm (12–40 inches)
Key Fact: This is the longest growth phase in the human body, allowing for significant length. Duration varies by genetics, health, and ethnicity.

Beard Hair:

Anagen Duration: 1–2 years
Average Maximum Length: 15–30 cm (6–12 inches)
Key Fact: Coarser than scalp hair, with a shorter but still multi-year growth phase.

Eyebrow & Eyelash Hair:

Anagen Duration: ~30–45 days
Average Maximum Length: 1–2 cm (0.4–0.8 inches)
Key Fact: The very short growth phase is a protective adaptation, preventing long hairs from obstructing vision or trapping debris.

Body Hair (Arms, Legs, Torso):

Anagen Duration: 30–90 days
Average Maximum Length: <2 cm (0.8 inches)
Key Fact: This brief growth phase results in the fine, short hairs characteristic of vellus or terminal body hair.

Pubic & Underarm Hair:

Anagen Duration: ~6 months
Average Maximum Length: 2.5–5 cm (1–2 inches)
Key Fact: Growth cycles are synchronized by hormonal changes and feature a curly texture.

💡 Human Potential & World Record

The documented potential for human hair length is significant. The world record, held by Xie Qiuping of China, measured 5.627 meters (over 18 feet) in 2004, grown across approximately 30 years. In practice, average uncut scalp hair rarely exceeds 100–120 cm due to breakage, trimming, or the natural conclusion of individual follicle cycles.

💡 Core Biological Principle:

Hair does not “stop growing” at a fixed length. It reaches its terminal length when its individual Anagen phase ends and the follicle enters the resting (Telogen) phase. This is why scalp hair can grow for meters over decades, while other hairs are self-limiting.

Comparison with Animal Hair (Fur) Cycles

Animal fur cycles are fundamentally different, often adapted for seasonal survival rather than continuous growth.

Most Cats & Dogs (e.g., Huskies, Labradors): Have very short Anagen phases (weeks to months). Their fur grows to a genetically preset length and then stops, followed by seasonal shedding.
Exception – Poodles: Similar to human scalp hair, Poodles have a long Anagen phase, meaning their fur will continue to grow if not clipped, a rare trait among mammals.

Evolutionary Insight:

Unlike human scalp hair, most mammal fur evolved with fixed-length growth cycles optimized for insulation and camouflage, not for producing long, continuous strands.

Ready for a Cycle-Based Hair Loss Analysis?

Effective treatment starts with diagnosing which phase of the hair cycle is predominantly affected in your case. Send clear photos of your scalp and a brief history for a free preliminary review. Our professional team will assess the patterns and recommend whether laser treatment or surgical intervention can work in harmony with your biology.

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Information on this website is provided for general educational purposes only and does not constitute personalized medical advice. It is not intended to promote our service or imply superiority over another.

Individual results in hair restoration vary significantly and no outcome can be guaranteed. The before-and-after images shown represent possible results — not promises. We recommend seeking independent medical advice to discuss your options … Read More

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