Hair Loss: Causes, Evidence and Treatment

Hair loss is a common medical problem with many possible causes. Most often it is genetically determined androgenetic alopecia, which arises from an increased sensitivity of the hair follicles to the hormone dihydrotestosterone (DHT). Nutrient deficiencies can also cause hair loss, but they are considerably rarer than often assumed. Stress, hormonal changes and certain conditions can affect the hair cycle as well. The best-evidenced treatments for genetic hair loss are topical minoxidil and, in men, finasteride. Many popular social media tips – biotin without a proven deficiency, or particular hair oils – have only limited scientific evidence behind them.

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What is normal hair loss?

Hair goes through a natural cycle of three phases:

1. Anagen phase (growth phase)

This phase typically lasts two to six years. About 85–90 % of hairs are in this phase at any one time.

2. Catagen phase (transition phase)

A short phase of about two to three weeks in which the hair follicle regresses.

3. Telogen phase (resting phase)

Lasts about two to three months. After that the hair falls out and a new hair grows in its place.

Losing 50–100 hairs a day is considered normal and corresponds to the physiological hair cycle.

Only when considerably more hair falls out, or bald patches appear, does medicine speak of alopecia.

The most common cause: androgenetic alopecia

Androgenetic alopecia is the most common form of hair loss.

According to epidemiological studies it affects:

• up to 50 % of men by the age of 50

• about 40 % of women over the course of their lives

Mechanism

Where there is a genetic predisposition, hair follicles react sensitively to dihydrotestosterone (DHT).

DHT is formed from testosterone by the enzyme 5-α-reductase.

The consequence:

shortening of the growth phase
miniaturization of the hair follicles
production of ever thinner hairs

This process happens over years to decades, which is why those affected often notice the changes late.

Stress-related hair loss (telogen effluvium)

Another common form is telogen effluvium.

Here many hairs move into the resting phase of the hair cycle at the same time.

Typical triggers are:

serious illness
surgery
severe psychological strain
pregnancy
infections
drastic weight loss
certain medications

The hair loss often appears 2–3 months after the triggering event.

Important:

In most cases this form is reversible once the body has stabilized.

Vitamin deficiency and hair loss

On social media, hair loss is frequently attributed to vitamin deficiency.

The scientific evidence, however, paints a more nuanced picture.

Some nutrients genuinely are relevant:

Iron

Iron deficiency is one of the most common nutrient deficiencies worldwide.

A low ferritin level can be associated with diffuse hair loss.

Vitamin D

Some studies show lower vitamin D levels in certain forms of hair loss.

Its role, however, is not yet fully understood.

Zinc

Zinc plays a role in cell division and hair follicle function.

Deficiency states, however, are relatively rare.

Biotin

Biotin is frequently marketed as the hair vitamin.

A genuine biotin deficiency, however, is very rare.

According to reviews, supplements are only of benefit where an actual deficiency exists.

Hormonal causes

In women in particular, hormonal changes can trigger hair loss.

Examples:

thyroid disorders
polycystic ovary syndrome (PCOS)
pregnancy and the postpartum period
menopause

Thyroid conditions can cause both diffuse hair loss and changes in hair structure.

Medication-related hair loss

Certain medications can also trigger hair loss, for example:

chemotherapy
anticoagulants
retinoids
certain antidepressants
beta blockers

In many cases this hair loss is reversible.

Evidence-based treatment options

Minoxidil

Minoxidil is a topical treatment that improves blood flow to the scalp and can extend the growth phase of the hair.

Randomized trials show significant improvements in hair density in androgenetic alopecia.

Finasteride

Finasteride inhibits the enzyme 5-α-reductase and thereby reduces DHT production.

Studies show:

slowed hair loss
partial regrowth

Finasteride is used above all in men.

Further treatments with growing evidence

Low-level laser therapy

Some studies show moderate improvements in hair density.

Platelet-rich plasma (PRP)

PRP treatments show positive effects in several studies, though the quality of those studies varies.

Myths from social media

Many popular tips so far have only limited scientific evidence:

rosemary oil
collagen preparations
hair gummies
„detox“ or special diets

Individual small studies exist, but large randomized trials are frequently missing.

When should hair loss be medically assessed?

A medical assessment is worthwhile in cases of:

sudden heavy hair loss
bald patches
hair loss in children
additional symptoms such as fatigue or weight loss
hair loss after starting a medication

Conclusion

Hair loss has many possible causes and can rarely be traced back to a single factor.

While genetic factors play the most common role, hormonal changes, stress or, more rarely, nutrient deficiencies can also be involved.

An evidence-based assessment is decisive in telling scientifically supported treatments apart from popular myths.

Sources

Sinclair R. Hair shedding in normal hair cycles.

Trüeb RM. Androgenetic alopecia.

Randall VA. Androgens and hair growth.

Rushton DH. Nutritional factors and hair loss.

Patel DP. Biotin for hair loss review.

Olsen EA. Topical minoxidil randomized trial.

Kaufman KD. Finasteride in androgenetic alopecia.

Jimenez JJ. Low-level laser therapy study.

Gentile P. PRP therapy in hair loss.

Disclaimer

This article is intended as evidence-based health education and does not replace individual medical advice.