Causes of Hair Loss: Complete Guide

Worried about shedding or thinning? This causes of hair loss guide sorts the science from the noise so you can spot patterns, discuss the right tests, and choose next steps with confidence. Most types are diagnosable—and many are treatable when you match therapy to the cause.

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See also:Stress & Lifestyle Triggers • Hormonal & Health Causes • Genetics & Hair Loss

How Dermatologists Approach Diagnosis

A board-certified dermatologist will start with history, scalp exam, pull test, and targeted labs. Getting the diagnosis right is the cornerstone of effective treatment—self-treating without a diagnosis can waste time (and hair).

Targeted tests your clinician may order (case-by-case):

• TSH ± free T4/T3: to screen for thyroid imbalance (common TE trigger).
• Ferritin/iron studies + CBC: low ferritin is frequently associated with TE.
• Vitamin D, B12, zinc: where diet/symptoms suggest.
• Scalp biopsy/dermoscopy: when scarring alopecia or mixed patterns are suspected.

Tip:pause high-dose biotin before thyroid testing; it can distort results. (See: Thyroid and Hair Loss: Symptoms & What to Test.)

The Big Three, Explained

1) Androgenetic alopecia (pattern hair loss)

• What you’ll notice: receding hairline and/or crown in men; widening part and diffuse top thinning in women.
• Why it happens: genetic sensitivity to androgens miniaturizes follicles over time.
• What to do: discuss topical minoxidil; men may consider finasteride/dutasteride under medical guidance; low-level laser, PRP, and (in selected, stable cases) hair transplantation. Transplant is for permanent pattern loss, not for temporary causes.

Thinking about surgery later? UK guidance notes hair transplant treats a diagnosable, hormonally mediated condition and should not be classed as mere cosmetic—underscoring the need for proper evaluation and qualified surgeons.

2) Telogen effluvium (TE)

• What you’ll notice: a sudden, even shed from all over the scalp, often 2–3 months after a trigger (illness, surgery, high fever, childbirth, crash diet, major psychological stress).
• Why it happens: more follicles shift into resting (telogen) at once; you may shed ~300 hairs/day at peak.
• What to do: identify and correct the trigger; check ferritin and thyroid; gentle hair care; most cases self-resolve within months. Chronic/relapsing TE warrants a dermatology review.

Iron connection: multiple studies associate low ferritin with TE; repleting iron when deficient can support recovery. (Your clinician will individualize thresholds.)

3) Alopecia areata (AA)

• What you’ll notice: round/oval bald patches with smooth skin; sometimes nail changes.
• What to do: see a dermatologist promptly—options include topical/injected corticosteroids and newer systemic therapies for extensive disease. AA often coexists with other autoimmune conditions.

Medications, Hormones & Health: What Belongs on Your Radar

• Hormonal shifts: postpartum, perimenopause, thyroid disease.
• Medications: chemotherapy (anagen effluvium), retinoids, some anticoagulants, β-blockers, isotretinoin, and others (ask your prescriber before making any change).
• Scalp disease: seborrheic dermatitis rarely causes major loss but can aggravate shedding; fungal infections (tinea capitis) require antifungals.

Treatment Pathways: Match The Therapy to The Cause

Evidence-based topicals/systemics

• Minoxidil for pattern loss and sometimes chronic TE.
• 5-alpha-reductase inhibitors (men) for pattern loss under supervision.
• Corticosteroids/other immunomodulators for AA per specialist.

Correct triggers & deficiencies

• Treat thyroid/iron issues; optimize nutrition and stress recovery.

Surgical options (select cases)

• FUT/FUE transplantation for stable pattern loss with adequate donor hair; not for active TE or AA. Choose credentialed teams and realistic plans.

What You Can Do This Week

• Document your pattern: photos in consistent lighting monthly.
• Check your triggers: illness, weight change, new meds, high stress in the past 1–6 months.
• Book a dermatology consult for diagnosis before starting treatments.
• Ask about labs: TSH/free T4 (± T3), ferritin/iron, ± vitamin D/B12/zinc as indicated.

See Top-Rated Clinics

Hair Enhancement Resources & Guides

• Common causes of hair loss
• Stress & Lifestyle Triggers for Hair Loss
• Hormonal & Health-Related Causes of Hair Loss
• How Genetics Influence Hair Loss

FAQ: Causes of Hair Loss Guide

Bottom Line

Getting results starts with a clear, clinically grounded diagnosis. Work with a dermatologist, investigate pattern vs. diffuse loss, and run smart labs (thyroid + iron when indicated). From there, align treatments—minoxidil/medical therapy for pattern loss, trigger correction for TE, and specialist care for AA. For surgery, wait until your condition is stable and choose accredited teams. This causes of hair loss guide is your starting point—see top-rated clinics here and keep learning with the resources above.

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References

• American Academy of Dermatology: Types, diagnosis & treatment of hair loss.
• Harvard Health Publishing: Hair loss & telogen effluvium overviews.
• StatPearls (NCBI): Telogen effluvium—evaluation, triggers, and hair-cycle basics.
• NHS: Who is (and isn’t) a candidate for hair transplant.
• BAAPS/BAPRAS/BAHRS statement on hair transplant as treatment for pattern loss.