AIMT Education Library

The Hair Growth Cycle: A Practitioner Education Overview

The normal hair follicle cycles through four recognized phases: anagen (active growth), catagen (regression), telogen (rest), and exogen (shedding of the old hair).

Reviewed under the AIMT evidence standard · 12 cleared sources · Practitioner education

Why the hair growth cycle matters

This overview is designed for beauty and scalp-care professionals who want a clear reference for the normal hair-growth cycle, its stages, typical timing, and normal variation.

Hair follicles don't move through the cycle in lockstep — each one progresses on its own timeline.

Understanding that baseline gives those observations context.

That's exactly why distinguishing normal cycle variation from abnormal cycling is relevant for practitioners assessing scalp health — and why making that distinction depends on objective morphological criteria.

The stages of the hair growth cycle

The numbers matter because they give the cycle scale.

In humans, scalp anagen typically lasts around 3 years, catagen around 3 weeks, and telogen around 3 months, and roughly 9% of scalp follicles are in telogen at any given time.

What professionals should understand

The cycle is more than a timetable.

That process is directed by hair follicle stem cells and the dermal papilla, coordinated through core signaling pathways such as Wnt, Sonic hedgehog, Notch, and BMP.

Everyday physiological factors — hormones, stress, nutrition, sleep, inflammation, and blood flow among them — can normally influence when that transition between growth and rest happens.

What this page can — and cannot — tell you

Scope: This page is limited to describing the normal hair growth cycle (anagen, catagen, telogen, exogen), its typical timing, underlying biology, and normal variation, for practitioner education purposes. It does not address diagnosis or treatment of hair-loss conditions, medication effects, or cosmetic/regenerative interventions, which are covered separately.

Much of the molecular detail describing cycle regulation comes from murine/animal models, and translation of these mechanisms to humans is not always fully confirmed.

Several foundational sources on the hair cycle are narrative reviews rather than systematic evidence syntheses, so the strength of underlying evidence varies across specific mechanistic claims.

Key takeaways

  • 01

    The normal hair follicle cycles through four recognized phases: anagen (active growth), catagen (regression), telogen (rest), and exogen (shedding of the old hair).

  • 02

    Because follicles cycle individually and asynchronously, distinguishing normal cycle variation from abnormal cycling requires attention to objective morphological criteria, which is relevant for practitioners assessing scalp health.

  • 03

    In humans, scalp anagen typically lasts around 3 years, catagen around 3 weeks, and telogen around 3 months, and roughly 9% of scalp follicles are in telogen at any given time.

Sources & references

The cleared source set supporting this page's evidence review.

  1. Xiangyu Lin, Liang Zhu, Jing He. Morphogenesis, Growth Cycle and Molecular Regulation of Hair Follicles2022 · doi: 10.3389/fcell.2022.899095
  2. Nicole Natarelli, Nimrit Gahoonia, Raja K. Sivamani. Integrative and Mechanistic Approach to the Hair Growth Cycle and Hair Loss2023 · doi: 10.3390/jcm12030893
  3. Xi-Min Hu, Zhi-Xin Li, Dan-Yi Zhang, Yi-Chao Yang, Shen-ao Fu, Zai-Qiu Zhang, Rong-Hua Yang, Kun Xiong. A systematic summary of survival and death signalling during the life of hair follicle stem cells2021 · doi: 10.1186/s13287-021-02527-y
  4. Jung Hyun Lee, Sekyu Choi. Deciphering the molecular mechanisms of stem cell dynamics in hair follicle regeneration2024 · doi: 10.1038/s12276-023-01151-5
  5. Ji Won Oh, Jennifer Kloepper, Ewan A. Langan, Yongsoo Kim, Joongyeub Yeo, Min Ji Kim, Tsai-Ching Hsi, Christian Rose, Ghil Suk Yoon, Seok-Jong Lee, John Seykora, Jung Chul Kim, Young Kwan Sung, Moonkyu Kim, Ralf Paus, Maksim V. Plikus. A Guide to Studying Human Hair Follicle Cycling In Vivo2016 · doi: 10.1038/jid.2015.354
  6. Marlon R. Schneider, Ruth Schmidt-Ullrich, Ralf Paus. The Hair Follicle as a Dynamic Miniorgan2009 · doi: 10.1016/j.cub.2008.12.005
  7. Kurt S. Stenn, Ralf Paus. Controls of Hair Follicle Cycling2001 · doi: 10.1152/physrev.2001.81.1.449
  8. Chew Teng Tan, Chin Yan Lim, Kenneth Lay. Modelling Human Hair Follicles—Lessons from Animal Models and Beyond2024 · doi: 10.3390/biology13050312
  9. Jingjing Wang, Chaoyu Fu, Sophie Chang, Christopher Stephens, Haimin Li, Dongmei Wang, Yuheng C Fu, Kathleen J Green, Jie Yan, Rui Yi. PIEZO1-mediated calcium signaling reinforces mechanical properties of hair follicle stem cells to promote quiescence2025 · doi: 10.1126/sciadv.adt2771
  10. Bing Zhang, Ting Chen. Local and systemic mechanisms that control the hair follicle stem cell niche2023 · doi: 10.1038/s41580-023-00662-3
  11. He-Li Zhang, Xi-Xi Qiu, Xin-Hua Liao. Dermal Papilla Cells: From Basic Research to Translational Applications2024 · doi: 10.3390/biology13100842
  12. Yi Zou, Fangqi Tang, Peiwen Li, Weiming Qiu, Mingxing Lei. Wnt10b Regulation of Hair Follicle Development, Regeneration, and Skin Diseases2025 · doi: 10.1007/s12015-025-10898-5

Related AIMT learning