What health problems cause hair loss is a question many people face when they notice unexpected shedding or thinning. Hair loss — medically termed alopecia — can be a visible indicator of an underlying health condition, from thyroid disorders and autoimmune diseases to nutritional deficiencies and hormonal imbalances. Identifying the root cause is essential, as many forms of hair loss are treatable once the trigger is found. This article explores the key medical conditions linked to hair loss, how they are diagnosed, and what treatment options are available on the NHS.

Common Health Conditions Linked to Hair Loss

Hair loss can result from autoimmune conditions, scalp infections, hormonal disorders such as PCOS, inflammatory scalp diseases, medication side effects, and significant physical or emotional stress.

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Hair loss, known medically as alopecia, can be a visible sign of an underlying health problem rather than simply a cosmetic concern. Understanding what health problems cause hair loss is an important first step towards finding the right treatment and support.

Several well-recognised medical conditions are associated with hair thinning or shedding:

• Alopecia areata – an autoimmune condition in which the immune system mistakenly attacks hair follicles, causing patchy hair loss on the scalp or elsewhere on the body.

• Scalp infections – fungal infections such as tinea capitis (ringworm of the scalp) can cause hair to break and fall out in affected areas. Tinea capitis is contagious, occurs most commonly in children, and requires systemic antifungal treatment rather than topical therapy alone.

• Lupus (systemic lupus erythematosus) – a chronic autoimmune disease that can cause diffuse hair thinning or patchy loss as part of its wider systemic effects.

• Polycystic ovary syndrome (PCOS) – a hormonal condition affecting people with ovaries, which can lead to androgenic (male-pattern type) hair thinning.

• Psoriasis and seborrhoeic dermatitis – inflammatory scalp conditions that may disrupt the hair growth cycle; shedding associated with these conditions is usually non-scarring and reversible with appropriate treatment, unless there has been secondary damage to the follicle.

• Traction alopecia – hair loss caused by prolonged tension on the hair from tight hairstyles (such as braids, ponytails, or extensions). When identified early and hairstyling practices are changed, this is often reversible.

• Trichotillomania – a condition in which a person repeatedly pulls out their own hair, resulting in irregular patches of loss; psychological support is a key part of management.

• Scarring (cicatricial) alopecias – a group of conditions, including lichen planopilaris and frontal fibrosing alopecia, in which inflammation destroys hair follicles and replaces them with scar tissue, causing permanent hair loss. These conditions require prompt specialist assessment to limit irreversible damage.

Certain medications can also trigger hair loss as a side effect. Chemotherapy agents typically cause anagen effluvium — rapid, widespread shedding of actively growing hairs — whereas other medicines, such as some anticoagulants (for example, warfarin), antidepressants, and beta-blockers, more commonly cause telogen effluvium, a diffuse shedding that develops weeks to months after starting treatment. Drug-induced hair loss is usually reversible once the causative medicine is stopped or changed, though patients should always consult their GP before making any changes to prescribed treatment. The risk and severity of hair loss varies considerably between individual medicines and patients; please refer to the patient information leaflet or the electronic Medicines Compendium (emc) for specific medicines.

Significant physical or emotional stress — including surgery, serious illness, or bereavement — can also cause a temporary form of diffuse shedding known as telogen effluvium, which typically resolves once the trigger has passed.

If you suspect a medicine is causing hair loss, or experience any other unexpected side effect, you can report this to the Medicines and Healthcare products Regulatory Agency (MHRA) via the Yellow Card Scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

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How Hormonal and Thyroid Disorders Affect Hair Growth

Both hypothyroidism and hyperthyroidism disrupt the hair growth cycle, causing diffuse thinning that often improves once thyroid hormone levels are stabilised with treatment.

Hormones play a central role in regulating the hair growth cycle, which consists of three phases: anagen (growth), catagen (transition), and telogen (resting/shedding). When hormonal balance is disrupted, hair follicles can be pushed prematurely into the resting phase, resulting in noticeable thinning or shedding.

Thyroid disorders are among the most common hormonal causes of hair loss. Both hypothyroidism (an underactive thyroid) and hyperthyroidism (an overactive thyroid) can affect hair texture and density. In hypothyroidism, reduced levels of thyroid hormones slow cellular metabolism, which can cause hair to become dry, brittle, and prone to falling out across the entire scalp. Hyperthyroidism, conversely, accelerates metabolic processes and can also disrupt the hair cycle, leading to diffuse thinning. Hair loss associated with thyroid conditions often improves once thyroid hormone levels are stabilised with appropriate treatment, though recovery may take several months.

Androgens — male sex hormones present in both men and women — are closely linked to a pattern of hair loss known as androgenetic alopecia (male- or female-pattern hair loss). In genetically susceptible individuals, the hormone dihydrotestosterone (DHT) binds to receptors in hair follicles, causing them to miniaturise progressively over time. This is the most common form of hair loss in adults. It is worth noting that sudden or diffuse hair loss in women is more likely to represent telogen effluvium than androgenetic alopecia; the two conditions have different patterns and management approaches.

Other hormonal changes that may contribute to hair loss include:

• Postpartum hair loss – a temporary telogen effluvium triggered by the sharp drop in oestrogen after childbirth. This is very common, usually self-limiting, and typically resolves within six to twelve months without specific treatment; reassurance is often the most important intervention.

• Menopause – declining oestrogen levels can unmask or worsen androgenetic alopecia in women.

• Adrenal disorders – conditions such as Cushing's syndrome, which involve excess cortisol, may also affect hair growth.

Nutritional Deficiencies and Their Role in Hair Loss

Iron deficiency is the most commonly identified nutritional cause of hair loss; deficiencies in vitamin D, zinc, biotin, and protein can also impair follicle function, but supplementation should only be started after confirmed deficiency.

Adequate nutrition is essential for healthy hair follicle function. Hair is one of the fastest-growing tissues in the body, and follicles have high metabolic demands. When the body is deprived of key nutrients — whether through poor diet, malabsorption, or restrictive eating — hair growth can be significantly impaired.

Iron deficiency is one of the most frequently identified nutritional associations with hair loss, particularly in women of reproductive age. Low ferritin (stored iron) levels have been associated with telogen effluvium, even in the absence of frank anaemia. It is important to note that this association is largely observational; the precise relationship between ferritin levels and hair loss is not fully established, and the benefit of iron supplementation for hair regrowth in the absence of confirmed deficiency has not been definitively proven. Where iron deficiency is confirmed, treatment should follow NICE and British Society for Haematology guidance.

Other important nutritional factors include:

• Vitamin D deficiency – vitamin D receptors are present in hair follicles, and low levels have been associated with alopecia areata and telogen effluvium in observational studies; however, the evidence for a causal relationship remains uncertain, and supplementation should be guided by confirmed deficiency rather than assumed benefit.

• Zinc deficiency – zinc supports protein synthesis and cell division; deficiency can cause diffuse hair thinning and is seen in conditions such as Crohn's disease or following bariatric surgery.

• Biotin (vitamin B7) deficiency – while rare, true biotin deficiency can cause hair loss; supplementation is only beneficial if a genuine deficiency is confirmed. Importantly, high-dose biotin supplements can interfere with a range of laboratory tests, including thyroid function tests and cardiac troponin assays, potentially leading to inaccurate results. The MHRA has issued a Drug Safety Update on this issue. Patients taking biotin supplements should inform their clinician and, where possible, pause high-dose biotin for an appropriate period before blood tests are taken.

• Protein deficiency – severely restricted protein intake, as seen in eating disorders or extreme dieting, can push hair follicles into the resting phase.

• Vitamin B12, folate, and coeliac disease – testing for these may be appropriate where there is clinical suspicion of malabsorption, a vegan or restrictive diet, or unexplained iron deficiency that does not respond to treatment.

Self-prescribing high-dose supplements without confirmed deficiency is not recommended and may carry risks. Patients should seek blood tests through their GP to identify specific deficiencies before starting supplementation.

When to See a GP About Hair Loss

See a GP if you experience sudden or patchy hair loss, scalp changes, hair loss alongside systemic symptoms, or signs of a scarring alopecia, as early assessment improves treatment outcomes.

Many people experience some degree of hair shedding — losing up to 100 hairs per day is considered within the normal range. However, certain patterns or accompanying symptoms warrant a consultation with a GP to rule out an underlying medical cause.

You should consider seeing your GP if you notice:

• Sudden or rapid hair loss over a short period

• Patchy bald areas on the scalp, beard, or eyebrows

• Hair loss accompanied by fatigue, unexplained weight changes, or feeling unusually cold or hot (which may suggest a thyroid problem)

• Scalp redness, scaling, itching, or soreness

• Hair loss alongside irregular periods, acne, or unwanted facial hair (which may indicate PCOS or another hormonal condition)

• Hair thinning following a new medication

• Significant emotional distress related to hair loss

• Signs that may suggest a scarring alopecia, such as scalp pain or burning, persistent redness, perifollicular scaling (scaling around individual hair shafts), or smooth shiny areas of scalp where follicular openings are no longer visible — these features warrant prompt referral to a dermatologist, as early treatment is important to prevent permanent hair loss

If you notice a boggy, tender, inflamed area of scalp (known as a kerion), which can occur as a severe inflammatory reaction to tinea capitis, seek prompt medical attention, as this requires urgent systemic antifungal treatment.

If you are concerned that tight hairstyles or chemical treatments may be contributing to hair loss, changing these practices early — before scarring occurs — can help prevent permanent damage.

Early assessment is particularly important because many causes of hair loss are treatable, and the sooner an underlying condition is identified, the better the outcome is likely to be. For example, correcting an iron deficiency or stabilising a thyroid disorder can lead to meaningful hair regrowth over several months.

Hair loss in children should always be evaluated by a healthcare professional, as it may indicate a scalp infection (such as tinea capitis) or alopecia areata requiring specific treatment. If your GP suspects a specialist condition, they may refer you to a dermatologist or an endocrinologist depending on the likely cause.

Diagnosis and Tests Used to Identify the Underlying Cause

Investigation typically includes a full blood count, serum ferritin, thyroid function tests, and targeted hormone or autoimmune tests, guided by clinical history and examination findings.

Identifying the cause of hair loss typically begins with a thorough clinical history and physical examination. Your GP will ask about the pattern and duration of hair loss, any recent illnesses, dietary habits, medications, family history, and associated symptoms. This information helps to narrow down the likely cause before any investigations are requested.

Common blood tests used in the investigation of hair loss include:

• Full blood count (FBC) – to check for anaemia and signs of infection or inflammation

• Serum ferritin (with C-reactive protein if inflammation is suspected) – to assess iron stores; ferritin is the preferred marker for iron deficiency, even when haemoglobin is normal. Transferrin saturation may be added if further assessment is needed. Serum iron alone is not recommended as a measure of iron status.

• Thyroid function tests (TFTs) – initial testing in UK primary care is TSH (thyroid-stimulating hormone); free T4 is added if TSH is abnormal. Free T3 is not a routine first-line test and is generally reserved for specialist use.

• Vitamin D levels – particularly relevant in individuals with limited sun exposure, darker skin tones, or other risk factors for deficiency

• Hormone profile – if PCOS or androgen excess is suspected, appropriate tests include total testosterone and sex hormone-binding globulin (SHBG) to calculate the free androgen index, and prolactin. LH/FSH ratio alone is not considered diagnostic for PCOS in current UK practice. If congenital adrenal hyperplasia is being considered, 17-hydroxyprogesterone may be measured.

• Inflammatory markers and autoimmune tests – such as CRP, ESR, and antinuclear antibodies (ANA), targeted to clinical suspicion of conditions such as lupus rather than performed routinely

If a fungal scalp infection is suspected, the appropriate investigation is mycology sampling using hair pluckings and scalp scrapings sent for microscopy and culture. Swabs are not adequate for diagnosing tinea capitis and should not be used for this purpose.

Patients taking high-dose biotin supplements should be advised to pause these before blood tests, as biotin can interfere with a range of laboratory assays and produce inaccurate results (MHRA Drug Safety Update).

In some cases, a GP may refer a patient to a dermatologist for more specialist assessment. A dermatologist may perform trichoscopy (dermoscopy of the scalp) to examine follicle structure and density, or in selected cases, a scalp biopsy to obtain a tissue diagnosis — particularly where a scarring alopecia is suspected. Testing is guided by clinical findings and should be targeted and clinically justified, in line with NICE CKS and British Association of Dermatologists (BAD) guidance, rather than performed indiscriminately.

Treatment Options Available on the NHS

NHS treatment targets the underlying cause — such as levothyroxine for hypothyroidism or iron supplementation for deficiency — with topical minoxidil and corticosteroids used for androgenetic alopecia and alopecia areata respectively.

Treatment for hair loss on the NHS depends entirely on the underlying cause identified during investigation. Where a specific medical condition is responsible, treating that condition is the primary goal, and hair regrowth often follows as a secondary benefit. It is important to have realistic expectations: hair regrowth is often slow, taking three to six months or longer to become visible.

Condition-specific treatments may include:

• Thyroid disorders – levothyroxine for hypothyroidism or antithyroid medicines (such as carbimazole) for hyperthyroidism, prescribed and monitored by a GP or endocrinologist. Carbimazole carries a small but serious risk of agranulocytosis (a dangerous reduction in white blood cells); patients should be advised to seek urgent medical attention if they develop a sore throat, mouth ulcers, or fever. Please refer to the patient information leaflet and the emc SmPC for full safety information.

• Iron deficiency – oral iron supplementation (such as ferrous sulphate) alongside dietary advice to increase iron-rich food intake, guided by confirmed blood test results.

• Alopecia areata – topical or intralesional corticosteroids are commonly used to suppress the localised autoimmune response. In more extensive or treatment-resistant cases, referral to a dermatologist is appropriate. Baricitinib (a JAK inhibitor, brand name Olumiant), has been approved by NICE for the treatment of severe alopecia areata in adults who meet specific criteria; its use is specialist-led, subject to NICE Technology Appraisal criteria, and requires careful monitoring given risks including serious infections, venous thromboembolism, and malignancy. Please refer to the NICE Technology Appraisal and the emc SmPC for full prescribing information.

• Scalp infections – tinea capitis requires systemic antifungal treatment; common options include oral terbinafine or griseofulvin, with the choice guided by the causative organism (identified on mycology). Antifungal shampoos may be used as an adjunct to reduce transmission but are not sufficient as sole treatment. Household contacts and close contacts (particularly in school settings) may need screening.

• Androgenetic alopecia – topical minoxidil is available over the counter and is the most widely used treatment for both men and women; side effects can include scalp irritation and unwanted facial or body hair growth. Finasteride 1 mg (for men) may be considered for androgenetic alopecia, but it is important to be aware that in the UK this is typically obtained via a private prescription and is not routinely funded on the NHS for hair loss. Finasteride is contraindicated in pregnancy, and women who are or may become pregnant should not handle crushed or broken tablets. The MHRA has issued a Drug Safety Update highlighting risks of sexual dysfunction (which may persist after stopping the medicine) and psychiatric effects including depression and suicidal ideation; patients should be counselled about these risks before starting treatment. Please refer to the BNF and emc SmPC for full prescribing and safety information.

• Telogen effluvium – management focuses on identifying and treating the underlying trigger (such as iron deficiency, thyroid disease, or significant stress), alongside reassurance that shedding is usually self-limiting. Recovery typically takes three to six months or longer after the trigger has resolved. General hair-care measures — such as avoiding tight hairstyles, minimising heat styling, and using gentle hair products — can help reduce additional stress on fragile hair.

• Scarring alopecias – treatment aims to halt progression rather than restore lost hair; early specialist referral is essential.

General measures and support: Camouflage products, hairpieces, wigs, and eyebrow prostheses can provide practical support for people affected by hair loss; some of these may be available on the NHS depending on the cause and clinical circumstances. Psychological support should not be overlooked — hair loss can significantly affect self-esteem and mental wellbeing. Referral to a counsellor or support organisations such as Alopecia UK may be beneficial alongside medical treatment.

If you experience a suspected side effect from any medicine used to treat hair loss, please report it to the MHRA via the Yellow Card Scheme at yellowcard.mhra.gov.uk or through the Yellow Card app. Patients are encouraged to discuss all available options openly with their GP or specialist.

Frequently Asked Questions