Hair Loss Causes and Why They Determine Treatment
What causes hair loss, and why does the cause determine which treatment works?
Hair loss looks like one problem in the mirror, but it's really a handful of separate conditions that happen to share a symptom. That's why naming the cause comes first: a DHT blocker won't touch an iron deficiency, and iron won't touch an autoimmune attack. The clock matters too, because most treatable causes have a window while the follicle is still alive, and that window closes quietly while you're applying the wrong product.
- Androgenetic alopecia: Inherited follicle sensitivity to DHT; the large majority of male loss.
- Telogen effluvium: A shock pushes follicles into rest; shedding surfaces two to four months later.
- Alopecia areata: Immune cells attack the follicle bulb, leaving sharply defined round patches.
- Scarring alopecias: Fibrous tissue replaces the follicle, and no topical or tablet brings it back.
Hair loss is a family of separate conditions, and a treatment only works when it opposes the specific mechanism driving the loss, which is why the cause has to be named before anything is applied.
What is androgenetic alopecia and how does DHT shrink a follicle over successive growth cycles?
This isn't hair falling out so much as hair being rebuilt smaller, cycle after cycle, until there's almost nothing left to see. Every follicle runs a growth phase of two to six years, a transitional phase of about two weeks, and roughly three months of rest before it starts over. In a susceptible follicle, each pass through that loop comes back a little thinner than the last.
- Conversion: 5-alpha reductase turns circulating testosterone into dihydrotestosterone, a far more potent androgen.
- Binding: That DHT locks onto receptors in the dermal papilla at the base of the follicle.
- Shortening: Each new cycle runs a briefer growth phase and rebuilds the bulb slightly smaller.
- Miniaturization: The thick terminal hair thins to a barely visible vellus hair, then stops coming in at all.
Androgenetic alopecia miniaturizes a follicle over successive cycles rather than killing it outright, so a follicle still producing fine hair can often be pushed back toward terminal growth while one dormant for years offers little to work with.
Why does a treatment that regrows hair for one cause do nothing at all for another?
Every treatment that works on hair does one narrow job: it interrupts a single step in a single mechanism. Take it off that mechanism and it isn't weak, it's inert, which is why the same product that changed someone else's scalp can do nothing measurable on yours.
| Treatment | What it interrupts | Where it does nothing |
|---|---|---|
| 5-alpha reductase inhibitor | Scalp DHT driving pattern loss | Shedding from floor-level ferritin |
| Immunomodulators | Immune attack on the follicle bulb | Hormonally miniaturized follicles |
| Nutrient correction | Deficiency-driven effluvium | Bloodwork that was already normal |
| Surgical relocation | Absence of a living follicle | Loss that hasn't been stabilized first |
A treatment only produces a result when it's matched to the mechanism actually causing the loss, and any treatment needs a full four to six month cycle before it can be judged, because visible density lags the biology by that long.
How is the underlying cause actually diagnosed before any treatment is chosen?
Diagnosis here is mostly careful looking, with a short list of targeted tests behind it. You're reading distribution first, then the scalp surface under magnification, then the timeline of the past few months. Get that order right and bloodwork becomes confirmation rather than a fishing expedition.
- Read the distribution: Temples and vertex point hormonal, round patches point autoimmune, diffuse shedding points to an effluvium.
- Look under magnification: Trichoscopy at twenty to seventy times shows whether shaft diameters vary and whether follicular openings survive.
- Run a pull test: A gentle tug on sixty hairs from several areas separates active shedding from a settled pattern.
- Take the history: Illness, surgery, crash diet, childbirth or a new prescription in the previous two to four months.
- Target the bloodwork: Ferritin, a full thyroid panel, complete blood count, and an androgen panel where other signs point that way.
Trichoscopy showing variable shaft diameter with follicular openings intact identifies miniaturization long before thinning is visible in the mirror, and the loss of those openings marks a scarring process that needs a biopsy rather than a growth product.
How does telogen effluvium differ from pattern loss, and why does it usually reverse on its own?
The shed that's frightening you now was usually set in motion by something that happened a season ago. This isn't a degraded cycle, it's a disrupted one: healthy full-sized follicles pushed into rest all at once, then released about three months later. Nothing has been destroyed, which is the whole reason it tends to right itself.
| Feature | Telogen effluvium | Pattern loss |
|---|---|---|
| Onset | Two to four months after a shock | Gradual over years |
| Shedding | Handfuls daily, well above the usual fifty to a hundred | Little visible shedding |
| Distribution | Diffuse, frontal hairline preserved | Temples and vertex, or a widening central part |
| Recovery | Density restored over six to nine months | Progressive without treatment |
Telogen effluvium resolves on its own within six to nine months once the trigger is removed, but a shed that keeps going points to a trigger still in place, such as untreated thyroid disease or continuing iron depletion.
How far does the stage of loss limit what any treatment can realistically achieve?
Stage sets the ceiling on what any treatment can reach, and no product moves that ceiling. One question decides everything: does the follicle still exist? A miniaturized follicle is alive and can be coaxed back, while one replaced by fibrous tissue is gone in the literal sense, and most people start later than they believe because a good share of the density in an area is already lost before thinning shows under ordinary light.
Nothing currently available regenerates a follicle that no longer exists, so the realistic goal shifts from regrowth to stabilization as loss advances, and the donor area is a fixed lifetime supply that no technique enlarges.
Which conditions destroy the follicle permanently instead of merely shrinking it?
This is the one category where waiting costs you hair you can't get back. When inflammation destroys the bulge region where the follicle's stem cells live, scar tissue takes the space and no drug, device or injection restarts it. Catching this early is worth more than catching any other cause.
- Lost follicular openings: The skin looks smooth and shiny where the small pores should be.
- Ringed inflammation: Redness or scale around individual follicles, sometimes several hairs from one opening.
- Symptoms you can feel: Burning, itching, tenderness or a crawling sensation, which non-scarring loss rarely produces.
- A moving edge: Frontal fibrosing recedes the hairline in a band; central centrifugal expands outward from the crown.
Once fibrous tissue replaces the follicle no drug, device, injection or serum can restart it, so a punch biopsy confirming a scarring alopecia should never be deferred, because treatment can only protect the follicles just outside the advancing edge.
What goes wrong when treatment is started on the wrong diagnosis?
The bill for a wrong diagnosis is paid in follicles, not in what the product cost. A mismatched treatment doesn't announce itself; it quietly does nothing for a year while the real process keeps running underneath. It can also mask something internal, since thinning is sometimes the first visible sign of anaemia, thyroid disease or an autoimmune condition.
Time on the wrong treatment is never neutral, because a scarring alopecia caught at eighteen months instead of three has permanently destroyed follicles in the interval that no later diagnosis recovers.
How do thyroid disease, iron deficiency and other internal problems show up in the hair?
Hair is expensive tissue to run and nothing depends on it, so your body cuts it loose early when resources or hormone signalling go off. That makes shedding a sensitive alarm, even if it's a vague one about what's actually wrong.
- Ferritin, not haemoglobin: Shedding is common below roughly thirty nanograms per millilitre, with many clinicians targeting above fifty.
- Thyroid runs both directions: Underactive gives coarse, brittle diffuse thinning; overactive gives fine, soft hair.
- Excess does harm too: Too much vitamin A or selenium is a recognised cause, so more isn't safer.
- Androgen excess in women: Polycystic ovary syndrome drives pattern-type thinning alongside irregular cycles and acne.
Correcting a deficiency doesn't stop shedding within weeks, because follicles have to re-enter the growth phase and then grow visible length, so improvement typically starts around three months after correction and density is restored over six to twelve.
Which medications and medical treatments cause shedding, and is that shedding reversible?
Drugs cause hair loss in two very different ways, and the timeline is what gives each one away. The abrupt kind is obvious. The quiet kind surfaces two to four months after you started something, which is long enough that most people never connect the two.
| Feature | Anagen effluvium | Drug-induced telogen effluvium |
|---|---|---|
| Typical cause | Cytotoxic chemotherapy | Anticoagulants, beta blockers, retinoids, some antidepressants |
| Onset | One to three weeks after the first cycle | Two to four months after starting |
| Extent | Abrupt, often near total | Diffuse thinning |
| Recovery | Begins three to six months after the last cycle | Density recovers over six to twelve months |
Drug-induced shedding is reversible once the medication is stopped or substituted, but no prescription should be stopped on suspicion alone, because the condition being treated almost always outranks the hair and a prescriber can usually find an equally effective alternative.
How do hairstyles, heat and chemical processing cause loss that no drug will fix?
This is the one category of hair loss you control completely, and it's the one most often left until it's permanent. Constant tension inflames the root, and if the pulling keeps up the follicle is eventually damaged and replaced with scar tissue. Breakage looks identical in the mirror but has nothing to do with the follicle at all.
A shed hair carries a small pale bulb at its end while a broken one has a blunt or frayed tip and no bulb, which is the at-home test that separates traction damage to the follicle from breakage along the shaft.
