Telogen effluvium, and why the cause is always months behind you

The pattern is almost always the same. Someone comes through a hard few months — a bad illness, a surgery, a bereavement, a birth, a period of not eating properly — and comes out the other side. Things settle. And then, just as life becomes manageable again, the hair starts coming out in handfuls.

It feels like the body has waited until the worst was over to break down. What is actually happening is a scheduling artefact, and once you see it, the whole thing becomes much less frightening.

The telogen effluvium mechanism

At any time, roughly 85 to 90% of your hairs are actively growing and about 10% are resting. The cycles are desynchronised, so shedding is continuous and unremarkable — the growth cycle guide has the full picture.

A significant physiological shock changes that. The body, prioritising, pushes a large batch of follicles out of the growth phase and into telogen simultaneously. Nothing visible happens at this point; the hairs are still sitting in their follicles, finished but held.

Telogen lasts approximately three months. At the end of it, all those hairs are released — together, in a group, over a few weeks. That is the shedding, and it arrives on a delay that has nothing to do with how you feel now.

The delay is the diagnostic feature. It is also why almost everyone blames the wrong thing: the shampoo they started six weeks ago is a far more available explanation than a fever in March.

The usual triggers

Look at the window two to four months before the shedding started, and check for:

• Illness with a high fever. Influenza and COVID-19 are both well-documented triggers.
• Surgery, especially under general anaesthetic.
• Childbirth. So common it has its own guide and its own timeline.
• Rapid weight loss or restrictive dieting. Particularly low protein intake, and increasingly relevant with GLP-1 medications, where fast loss is the point.
• Severe emotional stress — bereavement, divorce, a period of acute anxiety. This is real, and it is also over-attributed: everyone has stress, and most stress does not do this.
• Starting or stopping medication. Hormonal contraceptives in both directions, some antidepressants, retinoids, beta blockers, anticoagulants. Check the leaflet of anything you started in the window.
• Iron deficiency, which can develop slowly and has no obvious symptoms early on.
• Thyroid dysfunction, in either direction.
• Severe crash of any kind — significant blood loss, a serious infection, a hospital admission.

Write down what happened in that window. Roughly half the people who do this find something obvious that they had not connected to their hair.

What it looks like

Telogen effluvium is diffuse: thinner all over rather than in patches. You typically lose density at the part and around the hairline, but you do not develop bald spots. The hairs coming out have the small white bulb of a completed cycle rather than the tapered end of a break — check this first, because breakage is the other thing that produces alarming amounts of hair.

Daily loss might go from 80 to 300, sometimes more. It is dramatic in the shower and it is not usually as visible on your head as it feels.

Crucially: the follicles are intact. Nothing has been destroyed. They have been paused, and a paused follicle restarts.

The timeline

• Month 0 — the trigger.
• Months 2 to 3 — shedding begins, often abruptly.
• Months 3 to 6 — shedding continues, usually peaking early and tapering.
• Months 4 to 9 — regrowth. Short, fine new hairs appear, most visibly along the hairline and part. They stick up, they will not lie flat, and they are the best news in this whole guide.
• Months 9 to 18 — the new hairs reach a length where density looks normal again.

If the trigger has genuinely passed, this resolves. If the trigger is ongoing — an untreated thyroid problem, continuing restriction, chronic illness — it will not, because follicles keep being pushed into telogen.

What to do

Find the trigger and remove it if you can. This is the treatment. Everything else is supportive.

Get blood tests if there is no obvious cause. Full blood count, ferritin, thyroid function, and vitamin D as a standard first panel. Ferritin in particular: many people shed at levels a lab still reports as normal, and there is a reasonable clinical argument for treating ferritin under about 30 ng/mL in someone who is shedding. That is a conversation to have with a doctor rather than a supplement to self-prescribe.

Eat enough, and enough protein. Hair is a low-priority tissue and the body deprioritises it quickly during restriction. If your shedding followed a diet, the diet is the thing to change.

Do not overhaul your routine. There is nothing wrong with your shampoo, and a routine changed in a panic makes it impossible to interpret what happens next.

Be gentle mechanically. You cannot stop hair that has already been released, but you can avoid breaking the hair that is still attached, which is the last thing you need while density is down.

Photograph your part monthly. Both to catch regrowth early, which is enormously reassuring, and to have real evidence if you do end up seeing a dermatologist.

The hardest part is that the reassurance arrives late. You have to be patient across a period where you can see the loss and not the regrowth — and the regrowth is already happening under there, months before it is long enough to show.