The panic usually comes before the diagnosis. A man notices that the comb catches more than it used to, or that the temples look slightly higher than they did a year ago, or that a photograph shows something the mirror had been kind about. The instinct is to act immediately — new shampoo, supplement, a search history that ends in dread. The useful thing, first, is to slow down and identify what is actually happening. Hair thinning is rarely one thing, and the interventions that work for one cause do nothing for another.
Androgenetic alopecia: the chronic pattern.
Androgenetic alopecia (AGA) — male pattern baldness — is the most common cause of hair thinning in men, affecting approximately half of men by the age of fifty.1 The mechanism is well established: a genetically determined sensitivity to dihydrotestosterone (DHT) in certain follicles, primarily at the temples and crown, causes progressive miniaturisation of those follicles over years or decades. The hair shafts produced become progressively finer and shorter until the follicle produces no visible hair at all.2
The pattern is key. AGA follows recognizable distributions — the Hamilton-Norwood scale describes them. Recession at the temples, diffuse thinning at the crown, or both together. The back and sides of the scalp are typically spared because those follicles lack the same DHT sensitivity.3 If the thinning follows this pattern and the person has male relatives with similar patterns, the diagnosis is usually not difficult.
The two treatments with the most evidence are finasteride and minoxidil. Finasteride 1mg daily inhibits 5-alpha reductase, reducing DHT conversion, and produces stabilisation in approximately 83 to 90% of men and visible regrowth in around 65% at two years.4 It requires ongoing use; discontinuation results in resumption of loss within six to twelve months. Minoxidil, applied topically or taken orally at low dose, prolongs the anagen phase and increases follicular diameter.5 Used together, the two agents are more effective than either alone.6 Low-level laser therapy (LLLT) has credible if modest supporting evidence as an adjunct.7 Everything else, including most scalp serums, has either weak or no controlled trial data.
Telogen effluvium: the temporary shed.
Telogen effluvium (TE) is a diffuse, reactive shedding — the scalp's response to a physiological stressor that pushes a large proportion of follicles into the resting phase simultaneously.8 The trigger typically happened two to three months before the shedding becomes visible, because the follicle cycles through a resting phase before the hair is actually shed. This delay is the reason men often cannot identify the cause — they are looking at events from last month when the relevant event was three months ago.
Common triggers: illness with fever, surgery, crash dieting or significant caloric restriction, childbirth, thyroid dysfunction, iron deficiency, zinc deficiency, or sustained psychological stress.9 The shedding is diffuse — it comes from across the scalp rather than focusing on temples or crown — and the scalp itself usually looks normal. The hairs that come out have a visible white bulb at the root.
Acute TE resolves once the trigger is removed or treated, typically within six months, and the hair density returns to baseline. The treatment is identifying the trigger and addressing it — not buying a new shampoo. If the trigger persists, the shedding persists. For the relationship between sleep disruption and telogen effluvium specifically, see Sleep and the Scalp.10
Nutritional causes.
Iron deficiency is the most clinically significant nutritional driver of hair loss in men who present with diffuse thinning without a pattern consistent with AGA.11 The threshold matters: a serum ferritin below 40 ng/mL is associated with increased shedding even in the absence of anaemia. Supplementation in iron-deficient individuals produces measurable improvement in hair density, though response is slow — six to twelve months of adequate levels before significant regrowth is typical.11
Zinc deficiency produces a similar picture — diffuse shedding without a pattern — and responds to correction.9 B12 and folate deficiencies have weaker but plausible associations. Biotin deficiency, while frequently marketed as a cause of hair loss, is extremely rare in adults eating a normal diet; supplementation in biotin-replete individuals has no evidence of effect.12
Thinning that keeps you guessing — whether it is pattern, reactive, or something else — is easier to navigate with someone who can assess the full picture. Members have direct access to that kind of advisory.
Explore MembershipThe overlap problem.
The clinical reality is that AGA and TE frequently coexist. A man with underlying androgenetic alopecia may experience a TE episode that accelerates thinning at the temples — making what would have been a gradual process suddenly rapid. In this context, treating only the TE will bring the shedding back to the AGA baseline, not to full density. Understanding which component is present determines whether treatment ends at the acute trigger or whether longer-term management is appropriate.
The practical approach: if the shedding is sudden and diffuse and associated with a plausible trigger three months prior, start by addressing the trigger and checking ferritin, thyroid function, and basic nutrition. If the thinning is patterned — temples, crown — and has been present for more than a year, that is AGA and the window for maximum treatment response is now rather than later. And if the scalp itself is unhealthy — inflamed, flaking persistently, reactive — address the scalp environment first. Good follicles cannot do their best work on a compromised substrate.
When to stop researching and start acting.
The most expensive mistake in hair loss is the delay. AGA in particular is a condition where the follicle miniaturises progressively — a follicle that is miniaturising can be stabilised; a follicle that has completed the process cannot be recovered with any available non-surgical treatment. The window is real. The cost of six months of anxious research instead of a straightforward trial of finasteride is six months of miniaturisation that did not need to happen.