What Causes Hair Loss? Types, Causes and Best Treatments Explained
- Dr. Ryan Heals, Pharm.D.
- Jul 25
- 7 min read
Hair loss is one of the most emotionally significant health concerns affecting both men and women — and one of the most frequently misunderstood. Up to 80% of men and 50% of women will experience some form of pattern hair loss during their lifetime, according to research published in the National Library of Medicine. Yet many people spend years trying the wrong treatments because the type and cause of their hair loss was never correctly identified.
The critical starting point: hair loss is not one condition — it is many. Androgenetic alopecia (pattern hair loss), telogen effluvium (shedding triggered by stress or illness), alopecia areata (autoimmune), and traction alopecia (physical damage) all look and behave differently and require completely different treatment approaches. Getting the diagnosis right is the foundation of getting the treatment right.
This complete guide covers all major types of hair loss, their causes, how to identify which type you have, and the full range of evidence-based treatment options available in 2025.
The American Academy of Dermatology (AAD) Hair Loss Resource Center provides comprehensive dermatologist-reviewed guidance on all types of alopecia at: https://www.aad.org/public/diseases/hair-loss
Understanding the Hair Growth Cycle
Before examining hair loss types, understanding the normal hair growth cycle explains why and how hair loss occurs:
Anagen phase (growth):
Active hair growth — lasting 2–7 years per hair. The longer this phase, the longer the hair grows. Approximately 85–90% of scalp hairs are in anagen at any time.
Catagen phase (transition):
A brief 2–3 week transition phase in which the hair follicle shrinks and hair growth stops.
Telogen phase (resting/shedding):
The hair rests for 3 months before being shed and replaced. Normally 10–15% of hairs are in telogen — explaining the normal daily shedding of 50–100 hairs.
Exogen phase:
Active shedding of the telogen hair as the new anagen hair pushes it out.
Hair loss disorders disrupt this cycle in different ways — some shorten anagen (pattern hair loss), some push too many hairs into telogen simultaneously (telogen effluvium), and some destroy follicles entirely (scarring alopecias).
Type 1: Androgenetic Alopecia (Pattern Hair Loss) — Most Common
Who it affects:
Up to 80% of men and 50% of women over their lifetime. The most common form of hair loss by far.
What causes it:
Androgenetic alopecia (AGA) is caused by the action of dihydrotestosterone (DHT) — a potent androgen derived from testosterone by the enzyme 5-alpha reductase — on genetically predisposed hair follicles. DHT binds to androgen receptors in susceptible follicles, progressively miniaturising them: each growth cycle produces a shorter, thinner hair until the follicle eventually stops producing visible hair. The genetic susceptibility is polygenic — inherited from both maternal and paternal sides.
How it presents:
In men (male pattern baldness):
Receding hairline at the temples forming an "M" shape, thinning at the crown (vertex), eventually progressing to complete baldness in advanced cases. Classified by the Norwood-Hamilton scale (Stages I–VII).
In women (female pattern hair loss — FPHL):
Diffuse thinning at the crown and widening part line, with the frontal hairline typically preserved. Women rarely become completely bald. Classified by the Ludwig scale (Stages I–III)
Treatments:
Minoxidil (topical or oral)
the most widely used treatment for both men and women. Works by prolonging the anagen phase and increasing follicle size. Topical 2% or 5% applied daily; oral minoxidil (low-dose 0.25–5mg) is increasingly used. Effective in approximately 60% of users. Must be continued indefinitely — stopping reverses gains within 3–6 months.
Finasteride (men only)
oral 5-alpha reductase inhibitor that blocks DHT production. Reduces DHT by approximately 70%, slowing or stopping hair loss in 83% of men and producing regrowth in approximately 66%. Not approved for women of childbearing age due to teratogenic risk.
Dutasteride
a more potent 5-alpha reductase inhibitor approved in some countries (off-label in USA for AGA). Reduces DHT by over 90%.
Low-level laser therapy (LLLT)
FDA-cleared device therapy. Stimulates follicle metabolism. Modest but consistent evidence of benefit as monotherapy or adjunct.
Platelet-rich plasma (PRP) injections
scalp injections of concentrated growth factors from the patient's own blood. Growing evidence base particularly for early AGA.
Hair transplant surgery
follicular unit transplantation (FUT) or follicular unit extraction (FUE); permanent solution for stable pattern hair loss but does not prevent ongoing loss in non-transplanted areas.
Type 2: Telogen Effluvium — Shedding After Stress or Illness
Who it affects:
Very common, particularly in women. Usually temporary and reversible.
What causes it:
Telogen effluvium occurs when a significant physical or psychological stressor pushes a large proportion of hairs (up to 30%) simultaneously into the telogen (resting) phase. The trigger happens 2–3 months before the shedding begins — which is why patients often cannot identify a cause when the shedding starts.
Common triggers:
Childbirth (postpartum hair loss — one of the most common causes in women)
Major surgery or hospitalisation
Severe febrile illness — including COVID-19 (post-COVID telogen effluvium was widely reported from 2021 onwards)
Crash dieting or severe caloric restriction; iron deficiency
Thyroid dysfunction (both hypothyroidism and hyperthyroidism)
Starting or stopping hormonal contraceptives
Major psychological stress
Medications — including beta-blockers, anticoagulants, retinoids, anticonvulsants
How it presents:
Diffuse shedding across the scalp (not patchy), typically noticed in the shower or on pillows. The scalp is not inflamed. Parting may widen but significant bald areas are rare.
Treatment:
Address the underlying cause. Most telogen effluvium resolves within 6–12 months once the trigger is removed. Iron deficiency is the most important reversible nutritional cause to screen for and correct.
Type 3: Alopecia Areata — Autoimmune Patchy Hair Loss
Who it affects:
Approximately 1.7–2.1% lifetime prevalence. Can affect any age, including children.
What causes it:
Alopecia areata is an autoimmune condition in which T lymphocytes attack hair follicles, causing abrupt cessation of hair production. The exact trigger is unknown but genetic, immune, and environmental factors contribute. JAK (Janus kinase) signalling pathways play a central role — the basis for new JAK inhibitor treatments.
How it presents:
Sudden appearance of smooth, round or oval bald patches on the scalp or anywhere on the body
No inflammation, scarring, or symptoms in typical cases
Severity ranges from single small patches (alopecia areata) to complete scalp baldness (alopecia totalis) to loss of all body hair (alopecia universalis)
Nail pitting or ridging in approximately 10–66% of cases — a helpful diagnostic clue
Treatment:
Intralesional corticosteroid injections
first-line for limited patchy alopecia areata; most effective current treatment for localised disease
Topical corticosteroids
for less severe or paediatric cases
JAK inhibitors (baricitinib, ritlecitinib)
FDA approved for severe alopecia areata in 2022–2023; ritlecitinib (Litfulo) specifically approved for teens and adults. Most significant treatment advance in alopecia areata in decades.
Minoxidil
adjunct to stimulate regrowth once immune attack is controlled
Spontaneous remission occurs in up to 50% of patients with limited disease
Type 4: Traction Alopecia — Physical Damage
Traction alopecia results from chronic pulling tension on the hair follicle — from tight ponytails, braids, buns, weaves, or extensions. Initially reversible; becomes permanent with prolonged scarring. Prevention by avoiding sustained tension is the most effective strategy.
Hair Loss Types Quick Reference
Type | Pattern | Cause | Reversible? | First-Line Treatment |
Androgenetic alopecia (men) | Receding temples, crown | DHT + genetics | Partially — stabilises | Minoxidil + Finasteride |
Androgenetic alopecia (women) | Diffuse crown thinning | DHT + genetics | Partially | Minoxidil (topical or oral) |
Telogen effluvium | Diffuse shedding | Stress, illness, deficiency | Yes — usually | Address underlying cause |
Alopecia areata | Patchy, smooth | Autoimmune | Yes (in limited disease) | Intralesional steroids, JAK inhibitors |
Traction alopecia | Hairline recession | Physical tension | Yes if early | Stop traction hairstyles |
Scarring alopecia | Irregular loss with scarring | Inflammation, infection | No — permanent | Specialist dermatology |
Medical Conditions and Medications That Cause Hair Loss
Many systemic conditions and medicines cause hair loss — making medical evaluation important for any unexplained or diffuse hair loss:
Cause | Type of Hair Loss | Test / Action |
Iron deficiency anaemia | Telogen effluvium | Ferritin blood test — most important nutritional screen |
Hypothyroidism | Diffuse shedding | TSH blood test |
Hyperthyroidism | Diffuse shedding | TSH blood test |
Polycystic ovary syndrome (PCOS) | AGA-pattern + excess facial hair | Hormone panel (testosterone, DHEAS, LH/FSH) |
Lupus (SLE) | Patchy or diffuse — "lupus hair" | ANA, anti-dsDNA antibodies |
Zinc deficiency | Diffuse shedding | Serum zinc |
Biotin deficiency | Diffuse shedding | Rare — only screen if symptoms suggest |
Chemotherapy | Anagen effluvium — sudden complete loss | Expected — temporary |
Beta-blockers | Telogen effluvium | Discuss alternative with doctor |
Anticoagulants (warfarin, heparin) | Telogen effluvium | Usually mild — discuss if severe |
The NIH InformedHealth resource provides comprehensive evidence-based overview of hair loss causes and management at: https://www.ncbi.nlm.nih.gov/books/NBK279318/
Harvard Health Publishing provides a detailed guide specifically for female pattern hair loss at: https://www.health.harvard.edu/staying-healthy/treating-female-pattern-hair-loss
For our complete guide to Lupus (SLE) — an important medical cause of hair loss in women: [Lupus (SLE): Symptoms, Diagnosis and Treatment]
For our guide to thyroid conditions — a leading reversible cause of hair loss: [Hydroxychloroquine for Lupus and Rheumatoid Arthritis]
For our complete guide to Doxycycline — used in some scarring alopecia conditions: [Doxycycline 100mg Complete Guide]
Frequently Asked Questions
How many hairs is it normal to lose per day?
It is normal to shed 50 to 100 hairs per day as part of the natural hair growth cycle. Shedding that noticeably exceeds this — particularly diffuse loss throughout the scalp, large clumps in the shower, or a visibly widening part — warrants medical evaluation. Counting individual hairs is not practical; instead, monitoring the volume of hair in the shower drain or on pillows over several weeks is a useful indicator of change.
Can hair loss be reversed?
This depends entirely on the type and cause. Telogen effluvium — triggered by illness, stress, pregnancy, or nutritional deficiency — is almost always fully reversible once the underlying cause is addressed. Alopecia areata resolves spontaneously in up to 50 percent of limited cases. Androgenetic alopecia is not reversible but can be slowed or stabilised with Minoxidil and Finasteride, and miniaturised follicles can produce thicker hair with treatment. Scarring alopecias — where the follicle is permanently destroyed — are not reversible, making early diagnosis critical.
Does stress cause hair loss?
Yes — physical and psychological stress are established triggers for telogen effluvium, the most common form of stress-related hair loss. The mechanism is that stress hormones (particularly cortisol) prematurely shift growing hairs into the resting phase. Importantly, the shedding typically begins 2 to 3 months after the stressful event — so patients often cannot identify the cause when shedding starts. Chronic stress can also exacerbate androgenetic alopecia and alopecia areata.
Is Minoxidil safe for women?
Yes — topical Minoxidil 2% is FDA-approved for female pattern hair loss and has been used safely in women for decades. Low-dose oral Minoxidil is increasingly prescribed off-label for women with good tolerability. The main considerations for women are avoiding use during pregnancy and monitoring for unwanted facial hair growth with higher doses. Finasteride is generally not recommended for premenopausal women due to teratogenic risk.
When should I see a dermatologist for hair loss?
See a dermatologist if: hair loss is patchy or asymmetrical, the scalp is inflamed or scarred, shedding is severe or rapidly progressive, you have associated symptoms (fatigue, weight changes, hormonal symptoms), or over-the-counter treatments have not helped after 6 to 12 months. Early evaluation is particularly important for alopecia areata and scarring alopecias where prompt treatment prevents irreversible follicle loss.
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