Hair Loss in Men: What Causes It?
Male pattern baldness explains most hair loss — but not all of it. A clinician's guide to the causes, from DHT and genetics to stress, diet and thyroid.
Part of the Male Hair Loss Health Guide.
Key fact: Around 95% of hair loss in men is male pattern baldness, driven by the hormone DHT acting on genetically sensitive follicles. The remaining causes — stress, nutrition, thyroid problems and others — matter because many of them are reversible once identified.
How common is male hair loss?
Hair loss in men is far more common than many men realise before it happens to them. Around 66% of men experience noticeable hair loss by the age of 35, rising to over 85% by 50. Despite how common it is, many men delay seeking help — which matters, because the earlier hair loss is treated, the more effectively it can be managed.
95%
Of male hair loss is androgenetic alopecia
66%
Of men have noticeable loss by age 35
25%
Show early signs before age 21
Male pattern baldness (androgenetic alopecia)
The vast majority of hair loss in men — around 95% of cases — is male pattern baldness, also known as androgenetic alopecia. It follows a recognisable pattern: the hairline gradually recedes at the temples, thinning spreads across the crown, and over years the two areas may merge.
The condition is hereditary. If your father, grandfather or maternal uncles experienced significant hair loss, your own risk is elevated. But the genetic component is polygenic — it comes from multiple genes on both sides of the family — so patterns can skip generations or differ markedly between relatives.
Genetics
The strongest predictor. Inherited sensitivity to DHT causes follicle miniaturisation, from both maternal and paternal lines.
DHT
The key hormone. Derived from testosterone, it binds to follicle receptors in susceptible men and drives progressive shrinkage.
Age
The process can begin in the teens. By 21, around 25% of men with hereditary baldness show early signs.
Hormonal changes
Shifts in androgen levels, including from thyroid or other hormonal disruption, can accelerate genetic hair loss.
The role of DHT
Dihydrotestosterone (DHT) is a potent androgen created when the enzyme 5-alpha reductase converts testosterone. In men genetically predisposed to hair loss, DHT binds to androgen receptors in scalp follicles and gradually miniaturises them — each successive hair grows thinner, shorter and paler, until the follicle becomes dormant.
This is precisely why finasteride works so effectively: it inhibits 5-alpha reductase, reducing scalp DHT by up to 70% and halting the miniaturisation process.
Other causes of hair loss in men
Not all hair loss is genetic. When loss is sudden, patchy or diffuse rather than following the classic pattern, another cause is likely — and many are reversible:
| Cause | Type of hair loss | Reversible? |
|---|---|---|
| Telogen effluvium | Diffuse shedding across the whole scalp from stress, illness, surgery or crash dieting | Usually — resolves once the trigger is removed |
| Alopecia areata | Patchy loss caused by the immune system attacking follicles | Often, but unpredictable; needs specialist assessment |
| Nutritional deficiency | Thinning from low iron, zinc, protein or vitamin D | Usually — with dietary correction or supplementation |
| Thyroid conditions | Both under- and over-active thyroid can cause diffuse loss | Often — when the thyroid condition is treated |
| Medications | Some blood thinners, retinoids and antidepressants | Usually on discontinuation — consult your doctor first |
| Traction alopecia | Loss from hairstyles that pull persistently on the scalp | If caught early — stopping the traction allows recovery |
| Scarring alopecia | Rare conditions that permanently destroy follicles | No — requires specialist management |
Stress and hair loss
Significant physical or emotional stress can trigger telogen effluvium — a temporary condition where many follicles simultaneously enter the resting phase, causing widespread shedding, typically 2–3 months after the stressful event. It is common after illness, bereavement, surgery or extreme weight loss and usually resolves within 3–6 months. Chronic stress can prolong it. If you notice persistent diffuse shedding alongside anxiety, fatigue or low mood, speak to your GP.
Diet and nutritional deficiency
Hair follicles are metabolically active and need adequate nutrition. Deficiencies in iron (common in men who eat little red meat), zinc, protein and vitamin D are all associated with increased shedding. A blood test from your GP can identify deficiencies, which are usually straightforward to correct with dietary changes or supplements.
Worth knowing: supplements only help where there is a genuine deficiency. They do not treat genetic hair loss, because they do nothing about DHT — the hormone driving male pattern baldness.
When to see a doctor
See your GP promptly if: hair loss is rapid and diffuse (losing large clumps); you have patchy loss in a non-pattern distribution; loss comes with scalp itching, pain or visible redness; or you have unexplained weight change, fatigue or other symptoms alongside it. These can point to an underlying condition that needs investigation.
Treatment options
For the most common cause — male pattern baldness — there are two MHRA-approved treatments with strong evidence:
- Finasteride 1mg — a prescription oral tablet that blocks DHT production. First-line, with an 85% improvement rate over five years. See our finasteride guide.
- Minoxidil 5% — an over-the-counter topical that stimulates follicles directly, most effective combined with finasteride. See our minoxidil guide.
For non-genetic hair loss, treatment depends on the cause: correcting nutritional deficiencies, managing a thyroid condition, or reviewing a medication. The complete treatment guide covers every option, including transplants.
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Order Finasteride →Frequently Asked Questions
What is the most common cause of hair loss in men?
Male pattern baldness (androgenetic alopecia) accounts for around 95% of hair loss in men. It is caused by a genetic sensitivity to DHT — a hormone derived from testosterone that gradually miniaturises hair follicles, leading to progressive thinning and recession.
At what age do men typically start losing their hair?
Hair loss can begin as early as the late teens or twenties. Around 25% of men with hereditary hair loss notice it before age 21. By 35, approximately 66% of men have noticeable hair loss; by 50, this rises to over 85%.
Can stress cause hair loss in men?
Yes — significant physical or emotional stress can trigger telogen effluvium, where follicles enter a resting phase and shed excessively. This typically begins 2 to 3 months after the stressful event and resolves within 3 to 6 months once the stressor is removed.
Can hair loss from male pattern baldness be reversed?
Early-stage hair loss can often be significantly improved with finasteride. The earlier treatment starts, the better the outcome. Finasteride halts progression and can stimulate regrowth in follicles still capable of producing hair, but it cannot regrow hair from completely dormant or scarred follicles.
What is telogen effluvium?
Telogen effluvium is a temporary form of diffuse hair loss triggered by stress, illness, surgery, crash dieting or nutritional deficiency. Unlike male pattern baldness, it affects the whole scalp diffusely and usually resolves on its own once the underlying cause is addressed.
How do I know if my hair loss is genetic?
The classic signs are a receding hairline at the temples and thinning at the crown, following the Norwood scale pattern. A family history on either side significantly increases risk. A GP or prescriber can confirm the diagnosis and rule out other causes.
References
- NICE Clinical Knowledge Summaries. Alopecia — androgenetic. cks.nice.org.uk
- NHS. Hair loss. nhs.uk
- Cranwell W, Sinclair R. Male Androgenetic Alopecia. Endotext. 2016. ncbi.nlm.nih.gov
- Vary JC Jr. Selected Disorders of Skin Appendages — Acne, Alopecia, Hyperhidrosis. Medical Clinics of North America. 2015. pubmed.ncbi.nlm.nih.gov
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.