Telogen effluvium: the sudden hair loss that frightens and usually reverses

One day you look at your brush and there is twice as much hair as before. In the shower, on the pillow, when you tie your hair back. The fright is real and entirely understandable, but there is one thing worth knowing from the outset: the most common cause of diffuse hair loss is telogen effluvium, a form of non-scarring alopecia in which the follicle is not destroyed. It usually appears two to four months after a triggering event (childbirth, an illness, a hormonal change or a medication) and, in most cases, it resolves on its own. Here we explain what it is, why it happens and what the evidence says, with the nuances that matter.

What telogen effluvium is and why it happens

To understand it you need to look at the hair cycle. In a healthy scalp, around 85% of hair is in the growth phase (anagen) and approximately 15% in the resting phase (telogen). Anagen lasts almost four years; the resting phase, about four months. The system is deliberately out of sync: each hair follows its own rhythm, so day-to-day shedding goes unnoticed.

In telogen effluvium that balance is disrupted. An abnormally high number of follicles end the growth phase early and shift into resting all at once. Kligman described it as a premature termination of the anagen phase with an increase in hairs in telogen and diffuse shedding of club hairs. Under normal conditions you have that 85/15 split; in telogen effluvium up to 70% of the hairs in the growth phase can move into telogen, and shedding can affect up to 50% of the hair on the scalp. It sounds dramatic, but remember: these are hairs falling out to make room for new ones.

Here is the most reassuring fact, and one hardly anyone explains: the shedding shows up 2 to 4 months after the event that caused it and, paradoxically, in this type of hair loss, seeing hair fall out is a sign that new hair is pushing through. You are not losing the follicle; you are emptying the resting phase.

What triggers it

Telogen effluvium is the body's reaction to metabolic, hormonal or drug-related stress. Described triggers include normal physiology such as the postpartum period, certain medicines, serious infections, thyroid dysfunction, anaemia, trauma and emotional or physiological stress. Its exact prevalence is unknown and it can occur at any age, in either sex and in any ethnic group, although it is more common in women because of postpartum hormonal changes.

When it comes to medicines it is worth being precise, because this causes a lot of anxiety. Most drug-associated hair loss is of the telogen type and includes retinoids, beta blockers, calcium channel blockers, antidepressants and anti-inflammatories such as ibuprofen. Anagen effluvium is different: it is the abrupt shedding typical of chemotherapy agents (antimetabolites, alkylating agents, mitotic inhibitors), which affects hair in full growth and involves another mechanism.

There is also a documented nutritional component. In a cohort of women with telogen effluvium, ferritin was low in 46.5% of patients, 29.5% had iron deficiency, 5.8% had vitamin B12 deficiency and 0.6% folic acid deficiency. This is a single-centre observational study, so it shows a frequent association, not a universal causal relationship. And beware the easy conclusion: it has not been shown that taking vitamin supplements corrects hair loss when there is no genuine deficiency.

Acute and chronic: not the same thing

Telogen effluvium has two faces. The acute form is the classic one: it appears suddenly after an identifiable trigger, shedding spikes and it usually settles at around 3 to 6 months from onset, with spontaneous regrowth once the causative factor has been removed. The chronic form is more insidious and persistent, and the causes are often unclear, unlike in the acute episode.

As for the outlook, the underlying message is encouraging. Telogen effluvium is reversible, usually lasts less than six months and most people experience complete regrowth without treatment. The American Academy of Dermatology notes that most people see full regrowth around 6 to 8 months after the shedding begins. The key difference from scarring alopecias is that here the follicle is not destroyed: the factory is still intact.

What the evidence says about treatment

Here honesty is called for. There are no targeted treatments with solid evidence for telogen effluvium, and the exact mechanism by which physiological stress influences the human hair cycle remains unknown. Because the condition tends to reverse on its own, management focuses on identifying and correcting the trigger and giving the follicle time.

On topical minoxidil, which many people associate with any kind of hair loss, two things need clarifying. First: in Spain, topical minoxidil is indicated for the treatment of moderate androgenetic alopecia, not for telogen effluvium. Second: the specific evidence in telogen effluvium is limited to a single-arm open-label trial in 12 Japanese subjects (3 men and 9 women) who used 1 ml twice a day for 24 weeks. That is very limited data, not proof of efficacy.

To place the drug where it has actually been studied: in androgenetic alopecia, minoxidil has been shown to stimulate hair growth, although its exact mechanism is not fully understood; it induces hypertrophy of small follicles, prolongs the growth phase and speeds up the turnover of vellus follicles. In that indication, shedding stabilises in 4 out of 5 patients, with visible growth after 4 months or more of regular use. The dosage in the summary of product characteristics is 1 ml on the scalp twice a day, without exceeding 2 ml daily; it is not recommended in people under 18 or over 65 because of a lack of data, and on stopping it, growth may cease and return to the initial stage within 3 to 4 months. After application to intact skin, systemic absorption is low, on average 1.7% of the dose (range 0.3 to 4.5%). All of this describes its use in androgenetic alopecia; it is not a recommendation for your own case, which is for a doctor to assess.

What you can do in the meantime

Scalp care advice is gentle and common sense: avoid vigorous combing or brushing and intense massage. One myth worth dismantling with a fact: you are not advised to stop washing your hair. Washing does not cause the shedding; it simply gathers in the basin the hairs that were already in the resting phase and were going to fall out anyway. Spacing out washes does not slow anything down, it just bunches the shedding into a more visible moment.

In summary

What you need to take away is simple: telogen effluvium is frightening because it comes on so suddenly, but it is reversible, the follicle is not destroyed and most people recover their hair within a few months once whatever triggered it has been corrected. The key lies in identifying the cause, not in washing your hair less often or self-medicating. If the shedding worries you, goes on longer than expected or does not fit this pattern, in Spain there is now hair loss treatment with a prior assessment, a prescription where appropriate from a registered doctor and ongoing follow-up. You can check whether you are eligible.