Reviewed by Clare Devereux · IAT Certified Clinical Trichologist · July 2026

Telogen is the resting phase of the hair growth cycle. It lasts approximately three months, during which the hair remains in the follicle but is no longer growing. At the end of this phase, the hair is released — this is the shedding you see on your brush, your pillow, or in the shower. Losing 50 to 100 hairs a day is normal and simply reflects follicles completing their cycle on schedule. The clinical concern begins when a disproportionate number of follicles enter the resting phase at the same time.

What happens during the telogen phase

At any given time, around 10 to 15 per cent of the hair on your head is resting. The fibre is no longer being produced, but it stays loosely anchored in the follicle for about three months. During this period, the follicle is preparing beneath the surface — once the resting phase ends, a new strand begins to form at the root, eventually pushing the old hair out as it emerges.

This is the natural mechanism behind everyday shedding. Each follicle cycles independently, so the loss is staggered and invisible at normal volumes. You do not notice 80 hairs leaving across an entire day. What you do notice is when the stagger breaks — when hundreds of follicles enter the resting phase together, and the resulting wave of shedding arrives all at once.

When the balance shifts — telogen effluvium

When a significant proportion of follicles are pushed into the resting phase simultaneously, the result is a visible increase in shedding — typically appearing two to four months after the triggering event. This condition is called telogen effluvium. Common triggers include significant stress, illness, nutritional deficiency — particularly low ferritin — hormonal changes, and medication. (For a detailed clinical overview of the condition, see this StatPearls clinical reference.)

The shedding can feel alarming, but it reflects a disruption to the cycle — not permanent damage to the follicle. In most cases, the follicles will re-enter the active growth phase and new hair will follow, provided the underlying cause is identified and addressed. A trichologist assesses this using trichoscopy and blood biomarker analysis to separate the trigger from any pre-existing pattern of thinning that the shedding may have unmasked.

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Frequently asked questions

The resting phase typically lasts around three months. During this time, the hair sits in the follicle without growing. At the end of the phase, the hair is released and a new growth cycle begins in the same follicle.

It is a condition in which a large number of hair follicles enter the resting phase at the same time, leading to a noticeable increase in shedding two to four months later. It is usually triggered by a specific event — such as significant stress, illness, nutritional deficiency, or hormonal change — and in most cases it is reversible once the cause is addressed.

In the majority of cases, no. Because the follicles themselves are not damaged — they have simply entered the resting phase earlier than usual — new growth typically follows once the trigger is resolved. However, if an underlying condition remains unaddressed, the shedding can persist or recur. A trichologist can help identify the cause and determine whether other factors are contributing.

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IAT-Certified Clinical Trichologist

Clare Devereux

Clare is the founding clinical trichologist at Hair Health Essentials, practising in Dublin and London. With over a decade of clinical trichology experience underpinned by a lifetime in professional hair and scalp care, she specialises in personalised diagnostics — from trichoscopy and blood biomarker analysis to genetic testing — to identify what’s really happening with your hair and scalp.

Clinics: Blackrock, Dublin · Eden One, Dublin · Harley Street, London

Hair Health Essentials provides specialist trichological guidance. This content is for informational purposes and does not constitute medical advice. If you have concerns about your health, please consult your GP or medical practitioner.

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