Telogen hair loss causes are wide-ranging, spanning nutritional deficiencies, hormonal shifts, medical conditions, and psychological stress. Telogen effluvium — the most common form of diffuse hair shedding — occurs when a triggering event forces an abnormally high proportion of hair follicles into the resting phase simultaneously, leading to noticeable shedding weeks to months later. Understanding what drives this process is essential for effective diagnosis and recovery. This article explores the key causes of telogen effluvium, recognised hormonal and lifestyle triggers, when to seek NHS advice, and what investigations and treatments are available in the UK.

What Is Telogen Effluvium and How Does It Affect Hair Growth?

Telogen effluvium is a common form of diffuse hair loss in which a triggering event causes up to 30–50% of follicles to prematurely enter the resting phase, resulting in noticeable shedding two to four months later; follicles remain intact and regrowth is possible.

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Telogen effluvium is one of the most common forms of diffuse hair loss, characterised by an abnormal shift in the hair growth cycle. Under normal circumstances, approximately 85–90% of scalp hairs are in the anagen (active growth) phase at any given time, with only 10–15% resting in the telogen phase before naturally shedding. In telogen effluvium, a triggering event causes a disproportionate number of hair follicles — sometimes up to 30–50% — to prematurely enter the telogen phase simultaneously, resulting in noticeable shedding several weeks to months later.

The condition typically presents as diffuse thinning across the scalp rather than patchy or localised hair loss. Most people notice increased shedding when washing or brushing their hair, and loose hairs may be visible on pillows or in the shower drain. Importantly, telogen effluvium does not usually cause complete baldness; the follicles themselves remain intact and capable of regrowth once the underlying trigger is addressed.

There are two recognised forms: acute telogen effluvium, which resolves within six months, and chronic telogen effluvium, which persists beyond six months and may require more thorough investigation. Understanding the hair growth cycle is central to appreciating why there is often a delay of around two to four months — most commonly approximately three months — between the triggering event and the onset of visible hair loss. This delay can make identifying the cause particularly challenging for both patients and clinicians. Information from the British Association of Dermatologists (BAD), the Primary Care Dermatology Society (PCDS), and the NHS provides further detail on the natural history of this condition.

Common Medical and Nutritional Causes of Telogen Hair Loss

Thyroid disorders, iron deficiency, acute febrile illness (including COVID-19), chronic disease, and nutritional deficiencies such as zinc, vitamin D, and B12 are among the most common medical and nutritional causes of telogen effluvium in the UK.

A wide range of medical conditions and nutritional deficiencies are well-established triggers of telogen effluvium. Among the most frequently identified medical causes are:

• Thyroid disorders — both hypothyroidism and hyperthyroidism can disrupt the hair cycle; BAD and PCDS guidance supports thyroid function testing as part of the initial assessment for unexplained diffuse hair loss

• Iron deficiency — one of the most prevalent nutritional causes in the UK, particularly in women of reproductive age; low serum ferritin may be associated with telogen shedding, though the evidence base and optimal threshold vary; ferritin should be interpreted alongside clinical context and markers of inflammation

• Chronic illness — conditions such as systemic lupus erythematosus, inflammatory bowel disease, and chronic kidney disease can precipitate diffuse hair loss

• Acute febrile illness — significant infections, including COVID-19, have been widely reported to trigger telogen effluvium approximately two to three months after the acute illness

• Rapid or significant weight loss — crash dieting or bariatric surgery can deprive follicles of essential nutrients

Nutritional deficiencies beyond iron — including zinc, vitamin D, vitamin B12, and insufficient dietary protein — are also recognised contributors. Testing for these should be guided by individual dietary history and clinical risk factors rather than as a routine panel. Vegans and vegetarians may be at particular risk of B12 and zinc deficiency. Whilst biotin deficiency is sometimes cited in popular media, true biotin deficiency is rare in the UK and there is limited robust clinical evidence supporting biotin supplementation in the absence of confirmed deficiency. Importantly, the MHRA has issued a Drug Safety Update warning that high-dose biotin supplements can interfere with immunoassay-based laboratory tests — including thyroid function tests — potentially producing falsely abnormal results. Patients taking biotin supplements should inform their clinician and the laboratory before testing; local policy on pausing supplementation prior to blood tests should be followed.

Certain medicines are also documented causes of telogen hair loss, including anticoagulants (such as heparin and warfarin), retinoids, beta-blockers, and some antidepressants. This list is not exhaustive; the BNF and individual Summary of Product Characteristics (SmPC) documents should be consulted for specific medicines. If you suspect a medicine may be contributing to hair loss, discuss this with your GP or pharmacist rather than stopping treatment without advice. Suspected adverse drug reactions, including medicine-induced hair loss, can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Lifestyle, Stress, and Hormonal Triggers Recognised in the UK

Significant psychological stress, postpartum oestrogen decline, perimenopause, and stopping the combined oral contraceptive pill are recognised hormonal and lifestyle triggers of telogen effluvium, with postpartum shedding typically resolving within six to twelve months.

Psychological and physiological stress are among the most widely recognised triggers of telogen effluvium in clinical practice. Significant emotional stress — such as bereavement, relationship breakdown, or prolonged work-related pressure — can activate the hypothalamic-pituitary-adrenal axis, elevating cortisol levels and disrupting the normal hair growth cycle. The NHS acknowledges stress as a contributing factor to hair loss, though not all individuals under stress will develop telogen effluvium, suggesting individual susceptibility plays a role.

Hormonal changes represent another major category of triggers, particularly relevant to women in the UK:

• Postpartum hair loss is extremely common, typically beginning around three months after delivery as oestrogen levels — which had been sustaining hair in the anagen phase during pregnancy — rapidly decline. Shedding usually improves within six to twelve months without specific treatment

• Menopause and perimenopause are associated with hormonal fluctuations that can precipitate or worsen telogen shedding. It is important to note that female pattern hair loss (androgenetic alopecia) is also common at this life stage and may coexist with or mimic telogen effluvium; a dermatology assessment is advisable if the diagnosis is unclear

• Stopping the combined oral contraceptive pill may trigger a temporary episode of telogen effluvium in some individuals as the body readjusts to its natural hormonal rhythm, though this is not universal and the evidence base is limited; clinical review is recommended if concerns arise

Lifestyle factors such as poor sleep quality, excessive alcohol consumption, and smoking may also contribute to hair follicle stress, though the evidence for these associations is less robust than for nutritional or hormonal causes. Restrictive dietary patterns — increasingly prevalent in the UK — can compound nutritional deficiencies that predispose individuals to telogen hair loss. Addressing modifiable lifestyle factors is therefore an important component of both prevention and management.

When to See a GP or NHS Specialist About Hair Shedding

Consult a GP if hair loss is sudden, severe, persists beyond three to six months, is accompanied by systemic symptoms, or is causing significant psychological distress, as these features may indicate an underlying medical condition requiring investigation.

Some degree of daily hair shedding — typically 50 to 100 hairs per day — is entirely normal. However, certain features should prompt a consultation with a GP to rule out an underlying medical cause and to access appropriate support. You should consider contacting your GP if:

• Hair loss is sudden, severe, or rapidly progressive

• Shedding has persisted for more than three to six months without improvement

• Hair loss is accompanied by other symptoms such as fatigue, weight changes, palpitations, or skin changes that may suggest a systemic condition

• There are signs of androgen excess or menstrual irregularity (such as hirsutism or irregular periods), which may suggest polycystic ovary syndrome or another endocrine condition

• There is patchy or localised hair loss, which may indicate alopecia areata or another distinct condition requiring different management

• There are scalp symptoms such as pain, persistent redness, scaling, or pustules, which may suggest scarring alopecia — a condition requiring prompt specialist assessment to prevent permanent follicle damage

• In children, scaling of the scalp, broken hairs, 'black dot' appearances, or associated lymph node swelling may indicate tinea capitis (scalp ringworm), which requires antifungal treatment and prompt review

• Hair loss is causing significant psychological distress, as this in itself warrants professional support

• You are experiencing hair loss following a recent illness, surgery, or change in medication

GPs can initiate first-line investigations and, where appropriate, refer patients to an NHS dermatologist for specialist assessment. Trichologists — practitioners who specialise in hair and scalp conditions — are not medical doctors, and trichology is not a protected medical title in the UK; trichology services are typically available in the private sector rather than through the NHS. It is important not to self-diagnose or self-treat with supplements without professional guidance, as excessive intake of certain nutrients — such as vitamin A or selenium — can paradoxically worsen hair loss.

Diagnosis and Tests Used to Identify the Underlying Cause

Diagnosis involves a thorough clinical history and targeted blood tests — including full blood count, serum ferritin, and thyroid function tests — guided by individual risk factors; patients taking high-dose biotin must inform their clinician before testing due to risk of falsely abnormal results.

Diagnosing telogen effluvium is primarily a clinical process, supported by targeted investigations to identify the underlying cause. A thorough history is essential and should cover the timeline of hair loss, recent illnesses or stressors, dietary habits, medication use, menstrual history, and family history of hair loss. The pull test — gently pulling a small bundle of hairs from the scalp — can provide a useful bedside assessment; finding an increased proportion of telogen hairs (identifiable by their club-shaped, non-pigmented roots) suggests active shedding, though results should be interpreted alongside the clinical picture.

Blood tests are selected based on clinical suspicion and individual risk factors. In line with BAD and PCDS guidance, a typical baseline assessment may include:

• Full blood count — to assess for anaemia

• Serum ferritin — a marker of iron stores; low levels may be associated with hair loss, though optimal thresholds vary and results should be interpreted in the context of inflammation and the overall clinical picture

• Thyroid function tests (TFTs) — to exclude hypothyroidism or hyperthyroidism

• Vitamin D, vitamin B12, and folate — where dietary history or clinical risk factors indicate deficiency

• Zinc and inflammatory markers — where clinically indicated

• Hormonal profile (including androgens and prolactin) — if androgenetic alopecia, polycystic ovary syndrome, or other endocrine pathology is suspected

Patients taking high-dose biotin supplements should inform both their clinician and the laboratory before blood tests are taken, as biotin can interfere with immunoassay-based tests — including thyroid function tests — and produce falsely abnormal results (MHRA Drug Safety Update). Local policy on pausing supplementation prior to testing should be followed.

In specialist settings, trichoscopy (dermoscopy of the scalp) or scalp biopsy may be performed to differentiate telogen effluvium from other conditions such as androgenetic alopecia or scarring alopecia. Accurate diagnosis is critical, as the management of these conditions differs considerably.

Treatment Options and Recovery Outlook for Telogen Effluvium

Treatment centres on identifying and correcting the underlying cause; acute telogen effluvium typically resolves within six to twelve months, and no medicine is currently licensed specifically for this condition in the UK.

The cornerstone of treating telogen effluvium is identifying and addressing the underlying cause. In many cases, once the precipitating trigger is resolved — whether that is correcting a nutritional deficiency, treating a thyroid disorder, or managing stress — hair regrowth occurs naturally. For acute telogen effluvium, including postpartum hair loss, full or near-full recovery typically occurs within six to twelve months of the trigger resolving. Patients should be counselled that regrowth is gradual and may not be immediately apparent, which can be a source of significant anxiety.

Specific interventions depend on the identified cause:

• Iron supplementation is recommended where deficiency is confirmed. Oral ferrous sulphate is the standard first-line treatment on the NHS, typically providing approximately 65 mg of elemental iron per dose. Alternate-day dosing may improve absorption and tolerability for some patients. Duration of treatment and monitoring should follow British Society for Haematology (BSH) guidance and be guided by the underlying cause of deficiency

• Thyroid replacement therapy (levothyroxine) or antithyroid medication will be initiated by a GP or endocrinologist as appropriate

• Dietary optimisation — working with a dietitian to ensure adequate protein, zinc, and vitamin intake — is particularly important in those with restrictive diets

• Stress management — psychological support, cognitive behavioural therapy (CBT), or mindfulness-based approaches may be beneficial where stress is a primary driver

• Gentle hair care — avoiding excessive heat styling, tight hairstyles, and harsh chemical treatments can help minimise additional mechanical stress on fragile regrowth

There is currently no medicine licensed specifically for telogen effluvium in the UK. Topical minoxidil is licensed for androgenetic alopecia (male and female pattern hair loss) but is sometimes used off-label to support regrowth in telogen effluvium; the evidence for this specific use is limited. Minoxidil is not recommended during pregnancy or breastfeeding. Common adverse effects include scalp irritation and unwanted facial or body hair growth (hypertrichosis); rare systemic effects have been reported. Any consideration of off-label minoxidil use should involve a discussion with a qualified healthcare professional, with reference to the relevant Summary of Product Characteristics (SmPC).

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If you suspect that a medicine is causing or contributing to hair loss, do not stop treatment without seeking advice from your GP or pharmacist. Suspected adverse drug reactions — including medicine-induced hair loss — should be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

The overall prognosis for acute telogen effluvium is generally favourable. Chronic telogen effluvium may require longer-term monitoring and support, but it too is rarely permanent. Reassurance and patient education remain vital components of care throughout the recovery process.

Frequently Asked Questions