Health & Longevity Series · Medical education

The hair growth cycle

Anagen, catagen and telogen

3 min read

01Overview

How hair grows in cycles

Key takeaway for patientsShedding is part of the cycle. A sudden increase usually follows an event two to three months earlier, and patterned thinning has a hormonal and genetic basis; both can be assessed.

Each follicle works in a cycle. In anagen, the growth phase, which lasts years on the scalp, the follicle produces hair continuously. Catagen is a short transition in which growth stops. In telogen, the resting phase, the old hair is held and then shed as a new one begins.

At any time most scalp follicles are in anagen. A stress on the body can push many of them into telogen at once, causing diffuse shedding some months later. Androgens, in people who are genetically susceptible, gradually shorten anagen and shrink the follicles.

02Key steps

Key phases of the cycle

Anagen: The growth phase: cells in the matrix divide and the hair lengthens.
Catagen: A transition of a few weeks in which the follicle shrinks.
Telogen: A resting phase of a few months.
Shedding and renewal: The old hair is released, and stem cells in the bulge of the follicle start a new cycle.

03Factors in decline

Factors that disturb the cycle

The cycle responds to the state of the whole body:

Physiological stress: Illness, surgery, childbirth or rapid weight loss can trigger shedding.
Hormones: Androgens, thyroid disease and the menopause alter the cycle.
Nutritional deficiency: Low iron or protein.
Aging and genetics: Follicles shrink and anagen shortens.

04Clinical management

Clinical management and physician guidance

The pattern and the timing of hair loss point to its cause.

Clinical and laboratory assessment: The pattern and timing of loss, with ferritin, thyroid and hormone tests where indicated.
Physician-guided care: Decided by your physician, according to the cause.
Monitoring and follow-up: Over several months, because of the length of the cycle.

05Research focus

Research focus in the hair cycle

Core focus area	Biological target	Clinical relevance
Follicle stem cells	The bulge region	How a new cycle starts
Dermal papilla	Signaling to the hair matrix	Control of growth and of follicle size
Androgen action	Androgen receptors in the follicle	Patterned thinning of hair
Telogen shedding	Synchronized entry into rest	Diffuse hair loss after stress

06Questions

Frequently asked questions

Is daily shedding normal?: Yes. A proportion of follicles is always at the end of its cycle, so some hair is shed every day.
Why did my hair fall out months after I was ill?: Stress on the body moves many follicles into the resting phase together; the hair is shed two to three months later.
When should I see a physician?: For sudden, patchy or persistent loss.

07References

Academic references and literature

Paus R, Cotsarelis G (1999). The biology of hair follicles. N Engl J Med, 341(7), 491-7. PMID 10441606.
Stenn KS, Paus R (2001). Controls of hair follicle cycling. Physiol Rev, 81(1), 449-494. PMID 11152763.
Schneider MR, Schmidt-Ullrich R, Paus R (2009). The hair follicle as a dynamic miniorgan. Curr Biol, 19(3), R132-42. PMID 19211055.

This guide belongs to the Hair Growth program