Telogen Effluvium and Its Various Causes

Hair loss is a common phenomenon that can occur at any stage of life. As it is a symptom associated with various conditions and risk factors, its management requires a comprehensive diagnosis that identifies and addresses its underlying causes. Among the most frequent causes of hair loss are alopecia areata, androgenetic alopecia, and telogen effluvium.

In this article we will focus on telogen effluvium, reviewing its main causes, pathophysiology, relationship with various conditions, and current treatment options.

Table of Contents

1. Telogen effluvium — how do I identify it?
2. What factors trigger this condition?
3. Hormonal imbalances
4. Nutritional deficiencies
5. Is this reversible?
6. Frequently asked questions
7. References

1. Telogen Effluvium — How Do I Identify It?

Telogen effluvium is one of the most common causes of hair loss in patients attending their first consultation. It is characterised by excessive and diffuse hair shedding, with no visible signs of scalp disease and no follicular miniaturisation, which primarily distinguishes it from androgenetic alopecia.

But what can we do to halt the shedding? The key lies in timely diagnosis. During our consultations, we take a detailed medical history to identify possible triggering factors and carry out a scalp examination using a dermatoscope — an essential tool for accurate assessment and differential diagnosis. It is essential to request complementary tests to confirm the diagnosis and determine the most appropriate treatment.

2. What Factors Trigger This Condition?

Many factors can trigger the onset of telogen effluvium — from pharmacological treatments and episodes of physical stress, to environmental factors such as seasonal changes, travel, or even water quality.

However, beyond these general causes, it is particularly important to focus on certain common medical conditions. In our clinical experience, these are frequently identified incidentally during consultations, as in many cases they produce no obvious symptoms. Nevertheless, with sound diagnostic judgement, they can be readily identified and addressed in a timely manner.

3. Hormonal Imbalances

Among hormonal imbalances, thyroid hormones are particularly noteworthy. These play a fundamental role in human physiology, regulating key processes such as metabolism, cell regeneration, and the body’s energy balance. Their impact extends far beyond internal organs — the skin and hair are also directly influenced by their proper functioning.

When there is a thyroid disorder, such as hyperthyroidism or hypothyroidism, various clinical manifestations may appear. Among these, diffuse hair loss — present in up to 50% of patients — known as telogen effluvium, is particularly notable. In many cases, this hair loss can be one of the first clinical signs and should therefore not be overlooked.

When these processes are disrupted, the impact on hair can manifest in various ways:

• Generalised or diffuse hair loss.
• Changes in pigmentation, due to reduced melanin production and distribution.
• Decreased hair growth rate.
• Reduced production of new hair fibres, affecting hair density and volume.
• Dry, dull, and brittle hair, with a greater tendency to breakage.

4. Nutritional Deficiencies

Among nutritional deficiencies, iron deficiency anaemia stands out as a frequent cause of telogen effluvium. When the body lacks sufficient iron, hair weakens and shedding increases. This occurs because iron is essential for proper hair follicle growth; in its absence, many hairs prematurely interrupt their growth cycle and shed diffusely. High-risk groups include women of reproductive age with heavy periods, pregnant women, individuals with low-iron diets, and those with chronic conditions affecting intestinal absorption. Iron deficiency anaemia is considered when ferritin levels fall below 40–45 ng/mL.

Another highly prevalent deficiency is that of vitamin D. Higher-risk groups include office workers, older adults with limited mobility (and therefore reduced sun exposure), individuals following vegan diets, and pregnant women. Deficiency is considered when levels fall below 20 ng/mL.

This condition is common because vitamin D is difficult to obtain through diet alone, as very few foods contain it in significant amounts. For this reason, when adequate requirements are not met, oral supplementation represents a safe and effective alternative.

The hair-related manifestations associated with nutritional deficiencies include:

• Reduced hair density
• Increased fragility of the hair fibre
• Prolonged diffuse telogen effluvium
• Reduced hair growth rate

5. Is This Reversible?

In many cases, yes. Hair loss associated with the conditions described above is usually reversible once the hormonal or nutritional imbalance has been corrected. In fact, most triggers of telogen effluvium can be resolved if identified and treated in time.

However, it is important to bear in mind that hair regrowth occurs gradually, and full recovery can take several months after hormone levels have stabilised.

For this reason, we recommend consulting a specialist at the first signs of alopecia or upon noticing a significant increase in hair shedding. An accurate diagnosis, supported by the appropriate tests, is essential to identify the cause and establish the most effective treatment.

6. Frequently Asked Questions

How can I tell telogen effluvium apart from other types of alopecia?

It is characterised by diffuse and abundant hair shedding, with no clearly defined bald patches and no visible signs of scalp inflammation. Unlike androgenetic alopecia, there is no follicular miniaturisation, and the diagnosis is confirmed through clinical examination, dermatoscopy, and, in many cases, complementary tests.

What are the most common causes of telogen effluvium?

It can be triggered by multiple factors, including physical or emotional stress, illness, pharmacological treatments, seasonal changes, or travel. However, hormonal imbalances (such as thyroid disorders) and nutritional deficiencies — particularly iron or vitamin D deficiency — are especially significant.

Can a thyroid disorder cause hair loss?

Yes. Both hypothyroidism and hyperthyroidism can cause diffuse hair loss, known as telogen effluvium. In fact, it can be one of the first clinical signs, which is why thyroid function should be assessed in cases of persistent hair shedding.

Is telogen effluvium reversible, and how long does hair recovery take?

In most cases, yes. Once the underlying cause has been identified and treated, hair begins to recover progressively. However, the process is gradual and full recovery can take several months after the imbalance has been corrected.

This content has been prepared by the medical team at the Instituto Médico del Prado and reviewed by Dr. Bonilla Juárez and Dr. Gallardo Madrid.

Dr. Espinosa Custodio works at the Instituto Médico del Prado, his hair clinic in Madrid and in Mexico City. To book an appointment, you can contact us by phone at 912 468 664, via WhatsApp at 627 396 322, or through the contact page on our website. If you are calling from Mexico, our number is +52 55 4590 9909.

7. References

1. Aguero‑Zaputovich M, Aguilar Naville S. Efluvio telógeno: Revisión de la literatura. Gacet Dermatol. 2022 Aug 29. Available at: https://gacetadermatologicaspd.org.py/index.php/gac/article/view/143/121
2. Palma‑Peña S, Vivas‑O’Connor V. Efluvio telógeno. Piel. Form Contin Dermatol. 2024;39(8):487–494. doi:10.1016/j.piel.2023.12.021
3. Hussain F Asghar, Nazia Shamim, Umar Farooque, Haris Sheikh, Ramsha Aqeel. Telogen Effluvium: A Review of the Literature. Cureus. 2020;12(5):e8320. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7320655/
4. Karakoyun Ö, et al. Retrospective Review of 2851 Female Patients With Telogen Effluvium related study. PMC. 2025. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11826290/