Women's Health

Why Is My Hair Falling Out?

The Pin Health Staff Writer

September 25, 2026 9 min read

Hair loss is one of the most emotionally charged health changes a person can experience – and one of the most frequently dismissed. "It's stress." "It runs in the family." "It happens with age." Sometimes true. But often, there's a specific, measurable, and addressable cause sitting in your blood work that nobody has looked for.

Losing some hair daily is normal – the average person sheds between 50 and 100 hairs a day as part of the natural growth cycle. What’s not normal is when that shedding accelerates noticeably: more hair in the drain, more on the brush, a widening part, or thinning at the temples. These changes signal that the hair growth cycle has been disrupted – and the most common disruptors are hormonal and nutritional, not genetic.

How Hair Growth Actually Works – and Why It Stops

Each hair follicle cycles through phases: growth (anagen), transition (catagen), and rest (telogen), before the hair sheds and the cycle begins again. Disruptions to this cycle – from nutritional deficiencies, hormonal shifts, inflammation, or physical stress – push more follicles into the resting phase simultaneously, causing the diffuse shedding that often appears two to three months after the triggering event.

This delay is what makes hair loss so confusing. The thing that caused the shedding happened months ago – an illness, a surgery, a crash diet, a hormonal shift, a nutritional deficiency that developed gradually. By the time the hair loss is obvious, the original trigger has often resolved or been forgotten, making it harder to connect cause and effect.

Iron Deficiency: The Most Overlooked Cause

Low ferritin – the protein that stores iron – is the single most common correctable cause of hair loss in women, and among the most frequently missed. Hair follicles are highly sensitive to iron status because they’re among the most rapidly dividing cells in the body, requiring substantial iron for energy production and cell division.

The critical point is that ferritin falls long before hemoglobin – the marker of clinical anemia – is affected. A woman can have perfectly normal hemoglobin while carrying ferritin levels low enough to cause significant hair shedding. When her doctor orders standard blood work and reports her iron as normal, they may be measuring the wrong thing.

Testing ferritin alongside iron, TIBC, and iron saturation gives a complete picture of iron status. For women with hair loss, ferritin is the number that matters most – and raising it, through targeted supplementation and dietary change, frequently produces significant improvement in hair shedding over three to six months.

Thyroid Dysfunction: Hair Loss as a Hormone Signal

Both hypothyroidism and hyperthyroidism can cause hair loss – through different mechanisms, but with similar presentations: diffuse thinning across the scalp, sometimes including the outer third of the eyebrows in hypothyroidism.

Thyroid hormones directly regulate the hair growth cycle. Low Free T3 – the active thyroid hormone – slows the anagen (growth) phase and pushes more follicles into the resting phase. The result is diffuse shedding that doesn’t respond to topical treatments because the cause is systemic.

The challenge is that TSH alone – what most standard panels measure – can appear normal while Free T3 and Free T4 are declining. And thyroid antibodies (TPO and thyroglobulin) can be elevated for years before TSH shifts, indicating autoimmune thyroid inflammation that’s already affecting follicle function. A comprehensive thyroid panel is essential for anyone with unexplained diffuse hair loss.

Hormonal Shifts: PCOS, Androgens, and the Perimenopausal Transition

Androgenetic alopecia – pattern hair loss driven by sensitivity to androgens – affects women as well as men, though differently. In women it typically presents as diffuse thinning at the crown rather than a receding hairline. It’s driven by DHT (dihydrotestosterone) acting on genetically sensitive follicles – but the androgen levels that drive it are often in the normal female range. What matters is follicle sensitivity, not just absolute levels.

In women with PCOS, elevated androgens – reflected in elevated testosterone and DHEA-S – are a primary driver of hair thinning at the scalp alongside unwanted hair growth elsewhere on the body. The combination of scalp hair loss and facial or body hair growth is a classic androgenic pattern worth investigating.

During perimenopause and after menopause, the decline in estradiol and progesterone shifts the hormonal balance toward relative androgen dominance, even when absolute androgen levels remain normal. This is why many women notice hair thinning beginning in their forties – not because their androgens have risen, but because their estrogen, which previously balanced them, has declined.

Nutritional Deficiencies Beyond Iron

Hair follicles require a continuous supply of nutrients for their rapid cell division. Deficiencies in several key nutrients produce hair shedding through similar mechanisms – disruption of the growth cycle and impaired keratin synthesis.

Zinc is essential for DNA synthesis in follicle cells and the enzyme systems that regulate the hair cycle. Zinc deficiency produces diffuse hair shedding and is particularly common in people who eat little red meat, those with inflammatory bowel conditions affecting absorption, and people on restricted diets.

Vitamin D receptors exist in hair follicle cells, and deficiency – which is extraordinarily common – is associated with both diffuse hair loss and alopecia areata. The relationship between vitamin D and hair cycling is an active area of research, but the association is consistent enough that testing vitamin D is worthwhile in anyone with unexplained hair loss.

Vitamin B12 and folate are essential for the rapid cell division of hair follicles. Deficiency produces diffuse shedding that’s often accompanied by fatigue, pale skin, and neurological symptoms – though hair loss can be the presenting complaint before other symptoms develop.

Cortisol and Physical Stress: The Telogen Effluvium Trigger

Significant physical stress – a major illness, surgery, crash dieting, or prolonged psychological stress with elevated cortisol – can trigger telogen effluvium: a sudden shift of a large number of follicles into the resting phase simultaneously, producing dramatic diffuse shedding two to three months later.

Telogen effluvium is typically self-limiting – when the stressor resolves, the follicles gradually return to the growth phase. But when the underlying stress continues – whether physical (ongoing nutritional deficiency, unresolved illness) or hormonal (ongoing thyroid dysfunction, persistent insulin resistance) – the shedding continues and doesn’t resolve without addressing the root cause.

What Testing Reveals

A comprehensive hair loss panel should include ferritin alongside iron, TIBC, and iron saturation; a full thyroid panel with TSH, Free T3, Free T4, and thyroid antibodies; sex hormones including testosterone, DHEA-S, estradiol, and progesterone; zinc; vitamin D; vitamin B12 and folate; and cortisol.

This isn’t an exhaustive list – there are other causes of hair loss, including autoimmune conditions (alopecia areata), scalp conditions, and medications. But the blood panel described above identifies the most common correctable causes and does so before and independent of whether any other symptoms are present.

The pattern of findings matters as much as individual results. Low ferritin alongside elevated thyroid antibodies alongside low vitamin D is a different picture from elevated androgens alongside elevated fasting insulin – and points toward different interventions, even if the presenting symptom (hair shedding) looks the same.

What to Do

If you’re experiencing unexplained diffuse hair loss – particularly if it began or accelerated in recent months – a comprehensive blood panel is the most informative first step. Hair loss responds slowly to treatment; most people see improvement over three to six months once the underlying cause is addressed. That timeline makes early identification and intervention particularly valuable.

Ferritin deficiency responds to iron supplementation, though the form and timing matter for absorption. Thyroid dysfunction responds to medication or functional support depending on its nature. Hormonal imbalances may respond to dietary approaches, lifestyle modification, or medical treatment depending on their cause and severity. Nutritional deficiencies respond to targeted supplementation once the specific deficiency is identified.

What doesn’t work is topical treatment of a systemic problem. Shampoos, serums, and scalp treatments can support follicle health but cannot address the iron depletion, thyroid dysfunction, or hormonal imbalances driving the loss. The root cause – quite literally – is internal.

The Bottom Line

Hair loss is distressing – but for the majority of people who experience diffuse shedding, there’s a biological reason that’s identifiable through blood testing and addressable through targeted intervention. The dismissal of hair loss as purely genetic or inevitable leaves many people without the specific information they need to actually do something about it.

Your blood knows why your hair is falling out. The question is whether you’ve asked it.

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Key Takeaways

• Low ferritin is the most common correctable cause of hair loss in women – normal hemoglobin does not rule out iron depletion
• Both hypothyroidism and hyperthyroidism cause hair loss – a full thyroid panel beyond TSH is essential
• PCOS-related androgen elevation causes scalp thinning alongside excess body hair – testosterone and DHEA-S reveal this pattern
• Perimenopausal estrogen decline creates relative androgen dominance – explaining why hair thinning often begins in the forties
• Zinc, vitamin D, B12, and folate deficiencies all affect the hair growth cycle – nutritional status should be part of any hair loss workup
• Telogen effluvium appears two to three months after the triggering event – making cause-and-effect connections difficult without testing
• Topical treatments can’t address systemic causes – blood testing identifies what’s actually driving the loss