Why Is My Hair Falling Out? Hormonal Causes and What to Do

You are brushing your hair and more of it stays in the brush than seems right. Your shower drain is collecting clumps. Your part looks wider than it did six months ago. Maybe someone mentioned it. Maybe you noticed it in photos. However you got here, you are looking at your reflection and asking a question that millions of men and women ask every year: why is my hair falling out?

The default answer you will find online is genetics. And genetics does play a role in some forms of hair loss. But here is what most sources do not tell you: hair loss is frequently the first visible sign of an underlying hormonal, thyroid, or nutritional imbalance. Your hair follicles are some of the most metabolically active cells in your body. They are exquisitely sensitive to changes in hormones, nutrient availability, thyroid function, and stress. When something goes wrong internally, your hair is often the first thing to show it.

That matters because it means hair loss is not just a cosmetic problem. It is a diagnostic signal. And if you address the root cause rather than just treating the symptom, you can often reverse or significantly slow the loss while simultaneously improving the underlying condition that caused it.

This guide covers the major hormonal and nutritional causes of hair loss in both men and women, what to test, and which treatments actually work based on the clinical evidence. If your doctor has told you that your hair loss is "just genetic" without running a comprehensive hormone and nutrient panel, you may not have the full picture yet.

Hair loss is a signal, not just a cosmetic problem

Hair follicles cycle through three phases: anagen (active growth, lasting two to seven years), catagen (regression, lasting about two weeks), and telogen (resting, lasting about three months). At any given time, roughly 85 to 90 percent of your scalp hair is in the anagen phase. When something disrupts this cycle — a hormonal shift, a nutrient deficiency, a thyroid problem, a cortisol surge — a disproportionate number of follicles get pushed into the telogen phase prematurely. The result is diffuse shedding that typically appears two to three months after the triggering event.

This is why hair loss often lags behind its cause. The stressor may have happened months ago, which makes it harder to connect the dots. A thyroid that started underperforming in January may not produce visible hair loss until March or April. Postpartum hormonal changes that begin immediately after delivery typically manifest as hair shedding around three months postpartum.

The clinical takeaway is straightforward: if you are losing hair, something changed. Your job is to figure out what. And the most productive place to look is your hormones, your thyroid, and your nutrient status.

The hormonal causes of hair loss

Most forms of hair loss that are not purely genetic have a hormonal driver. Here are the most common ones, in rough order of how frequently they go undiagnosed.

Low thyroid function

Hypothyroidism is the single most underdiagnosed cause of hair loss, particularly in women. Your thyroid gland controls the metabolic rate of virtually every cell in your body, including hair follicle cells. When thyroid hormone output drops, follicle metabolism slows, the growth phase shortens, and more hairs enter the resting phase simultaneously. The result is diffuse thinning across the entire scalp — not the patterned loss you see with androgenetic alopecia, but a general reduction in density and volume.

What makes thyroid-related hair loss particularly frustrating is that it often occurs at TSH levels that most doctors call "normal." The standard reference range extends up to 4.5 or even 5.0 mIU/L, but many endocrinologists consider optimal TSH to be between 0.5 and 2.0 mIU/L. A patient with a TSH of 3.8 may be told everything looks fine while experiencing significant hair loss, fatigue, and weight gain. If your hair is thinning and you have not had a complete thyroid panel, that should be your first step.

Low iron and ferritin

Iron deficiency is the most common nutritional cause of hair loss worldwide, and it does not require full-blown anemia to affect your hair. Ferritin, the stored form of iron, is the critical marker. Hair follicle matrix cells are among the most rapidly dividing cells in the body, and they require adequate iron to synthesize DNA and maintain the growth phase. Multiple studies have found that women with unexplained hair loss have significantly lower ferritin levels than controls, and that hair regrowth occurs when ferritin is repleted above 40 to 70 nanograms per milliliter.

This is especially relevant for premenopausal women, who lose iron through menstruation, and for anyone with digestive issues that impair iron absorption. If your ferritin is below 40, supplementation is worth discussing with your provider even if your hemoglobin and hematocrit are normal.

PCOS and high androgens in women

Polycystic ovary syndrome affects up to 10 percent of women of reproductive age, and hair changes are among its hallmark features. The elevated androgens (particularly testosterone and DHEA-S) that characterize PCOS can cause both hirsutism (excess hair growth on the face and body) and androgenetic alopecia (thinning on the scalp, particularly at the crown and along the part line). The mechanism is the same as male pattern baldness: testosterone converts to DHT via the enzyme 5-alpha reductase, and DHT miniaturizes susceptible hair follicles on the scalp.

Addressing PCOS-related hair loss requires reducing androgen levels through a combination of insulin sensitization, anti-androgen medications like spironolactone, and in some cases, oral contraceptives. Treating just the hair without addressing the underlying hormonal imbalance produces disappointing results.

DHT and male pattern baldness

Androgenetic alopecia in men is the most well-known form of hair loss, and its primary driver is dihydrotestosterone (DHT). DHT is produced from testosterone by the enzyme 5-alpha reductase, and it binds to androgen receptors in genetically susceptible hair follicles on the scalp, causing them to progressively miniaturize. The result is the familiar pattern: recession at the temples, thinning at the crown, and eventual progression to significant baldness.

While genetics determine your susceptibility, DHT levels are modifiable. Finasteride blocks 5-alpha reductase and reduces serum DHT by approximately 70 percent, which slows or halts progression in the majority of men who take it. The genetic component determines whether you have susceptible follicles; the hormonal component determines how aggressively those follicles are attacked. Addressing the hormonal component can make a meaningful difference even in men with strong genetic predisposition.

Postpartum hair loss

During pregnancy, elevated estrogen extends the anagen (growth) phase of the hair cycle, which is why many women experience thicker, fuller hair during the second and third trimesters. After delivery, estrogen drops rapidly, and all of the follicles that were held in the growth phase transition into telogen simultaneously. The result is dramatic shedding that typically begins around three months postpartum and can last for several months.

Postpartum hair loss is physiologically normal and almost always self-limiting. Most women see full regrowth within six to twelve months. However, if shedding persists beyond twelve months or is accompanied by fatigue and weight changes, postpartum thyroiditis should be ruled out, as thyroid dysfunction after delivery is common and frequently missed.

Menopause and declining estrogen

The hormonal shifts of menopauseaffect hair in multiple ways. Declining estrogen reduces the duration of the growth phase and decreases overall hair density. Simultaneously, the relative increase in androgens (since estrogen is no longer balancing them) can trigger female pattern hair loss at the crown and part line. Many women in perimenopause and menopause notice their hair becoming thinner, drier, and more brittle — changes that often coincide with other menopausal symptoms like hot flashes, sleep disruption, and mood changes.

Hormone replacement therapy that restores estrogen and progesterone can help slow or partially reverse menopausal hair changes in many women. This is one of the many reasons that a comprehensive evaluation of menopausal symptoms should include hair as part of the clinical picture.

Cortisol and telogen effluvium

Chronic stress elevates cortisol, and elevated cortisol is one of the most common triggers of telogen effluvium. The mechanism is direct: cortisol signals the body to divert resources away from non-essential functions (like hair growth) toward acute survival needs. It also impairs the absorption of nutrients critical for hair health, reduces blood flow to the scalp, and disrupts the hormonal environment that hair follicles need to maintain their growth cycle.

Stress-related hair loss is particularly insidious because the stress itself often goes unrecognized as a medical issue. Patients are told to "manage their stress" without being given concrete interventions. Meanwhile, their cortisol remains elevated and their hair continues to thin. Measuring cortisol through a four-point salivary test and actively treating the elevation — not just suggesting relaxation — is a more productive approach.

Thyroid hair loss: the most underdiagnosed cause

Thyroid-related hair loss deserves its own section because of how frequently it is missed. The standard approach at most primary care offices is to check TSH alone and call it normal if it falls within the reference range. But TSH is a pituitary hormone, not a direct measure of thyroid hormone activity at the tissue level. You can have a TSH of 3.0 (which most labs call normal) while your free T3 is at the bottom of the range and your hair follicle cells are functionally hypothyroid.

A complete evaluation requires TSH, free T4, free T3, reverse T3, and thyroid antibodies (TPO and thyroglobulin). Hashimoto's thyroiditis — an autoimmune condition where the immune system attacks the thyroid gland — is the most common cause of hypothyroidism in developed countries and can cause hair loss even before TSH becomes overtly abnormal. Thyroid antibodies can be elevated for years before TSH rises out of range, and during that period, hair loss may be the primary symptom.

If you are losing hair and have not had thyroid antibodies checked, you may be missing the diagnosis. And if you are already on thyroid medication but still losing hair, your dose may need adjustment or you may need to add T3 to your regimen. Many patients on levothyroxine (T4 only) continue to experience hair loss because they are poor converters of T4 to the active T3 form.

What to test if your hair is falling out

A thorough workup for unexplained hair loss should include the following labs. If your doctor has only checked a CBC and a basic metabolic panel and told you everything is fine, you have not been adequately evaluated.

Thyroid panel:TSH, free T4, free T3, reverse T3, TPO antibodies, and thyroglobulin antibodies. This is the minimum for a complete thyroid evaluation. TSH alone misses subclinical hypothyroidism and Hashimoto's in early stages.

Iron and ferritin: Serum iron, ferritin, TIBC, and transferrin saturation. Ferritin below 40 nanograms per milliliter is insufficient for optimal hair growth even if your hemoglobin is normal. Target ferritin of 70 or above for hair restoration.

Vitamin D: 25-hydroxyvitamin D. Vitamin D receptors are present on hair follicle cells, and deficiency (below 30 nanograms per milliliter) has been associated with alopecia areata and telogen effluvium. Optimal range is 50 to 80 nanograms per milliliter.

Hormones: Total and free testosterone, DHEA-S, estradiol, and progesterone. In women, elevated androgens suggest PCOS. In men, the testosterone-to-DHT ratio can indicate whether DHT-mediated follicle miniaturization is accelerated.

Cortisol: A four-point salivary cortisol test maps your diurnal cortisol curve and reveals whether chronic stress is contributing to your hair loss. A single morning serum cortisol is less informative because it only captures one point in the 24-hour cycle.

Treatments that actually work

The most important principle of treating hair loss is to identify and address the root cause first. Applying topical treatments to hair that is falling out because of an untreated thyroid condition or iron deficiency is like mopping the floor while the faucet is running. Fix the faucet first.

Address the root cause

If your thyroid is underactive, optimizing thyroid medication to bring free T3 and free T4 into the upper half of the reference range will often stop the shedding and promote regrowth within three to six months. If your ferritin is low, iron supplementation (typically 65 milligrams of elemental iron with vitamin C for absorption, taken on an empty stomach) should raise ferritin to a hair-supportive level within two to three months. If cortisol is elevated, the interventions described in our cortisol guide should be implemented. If PCOS is driving elevated androgens, insulin sensitization and anti-androgen therapy should be initiated.

Minoxidil

Minoxidil (Rogaine) is the most well-studied topical treatment for hair loss in both men and women. It works by extending the anagen phase and increasing blood flow to the follicle. The 5 percent foam formulation applied once or twice daily produces measurable regrowth in approximately 40 to 60 percent of users over 12 months. It does not address the root cause of hair loss, but it is a useful adjunct while the underlying condition is being treated.

Finasteride

Finasteride (Propecia) blocks 5-alpha reductase and reduces DHT by approximately 70 percent. It is the most effective medical treatment for male androgenetic alopecia, slowing progression in about 90 percent of men and producing regrowth in about 65 percent. However, it requires caution: a small percentage of men experience sexual side effects including reduced libido, erectile difficulty, and decreased ejaculate volume. These side effects are dose-dependent and reversible in most cases upon discontinuation, but they are real and should be discussed with your prescribing physician. Finasteride is not approved for use in premenopausal women due to teratogenicity.

Peptides: GHK-Cu for hair

GHK-Cu (copper peptide) is a naturally occurring tripeptide that has shown promise for hair restoration in preliminary research. It stimulates hair follicle growth by increasing the size of hair follicles, upregulating growth factors including VEGF and FGF, and promoting angiogenesis (new blood vessel formation) around follicles. GHK-Cu also has anti-inflammatory properties that may benefit the scalp environment. It is available as a topical serum or through mesotherapy injections directly into the scalp. While the evidence base is still growing, early clinical results are encouraging, particularly when combined with other treatments.

PRP (platelet-rich plasma)

PRP therapy involves drawing your blood, concentrating the platelet-rich fraction, and injecting it into the scalp. Platelets release growth factors that stimulate follicle activity and promote hair growth. Multiple randomized controlled trials have shown that PRP produces statistically significant improvements in hair density and thickness compared to placebo. It is most effective for androgenetic alopecia and telogen effluvium, and it works well as a complement to medical treatments like minoxidil and finasteride.

Nutritional support

Beyond iron, several nutrients are important for hair health. Biotin (B7) is the most commonly supplemented, though evidence for its benefit is strongest in cases of actual biotin deficiency, which is relatively uncommon. Zinc deficiency can cause hair loss and should be corrected if present. Vitamin D should be optimized to 50 to 80 nanograms per milliliter. Omega-3 fatty acids support scalp health and reduce inflammation. A comprehensive nutrient panel is more productive than blindly supplementing individual vitamins.

Frequently asked questions

How much hair loss is normal per day?

Losing 50 to 100 hairs per day is considered physiologically normal. What matters is whether you notice a change from your personal baseline. If you are suddenly finding more hair on your pillow, in the drain, or in your brush than usual, that is worth investigating — regardless of whether the absolute number exceeds a textbook threshold.

Can thyroid problems cause hair loss?

Yes, and thyroid dysfunction is one of the most underdiagnosed causes. Both hypothyroidism and hyperthyroidism disrupt the hair growth cycle. Many patients with thyroid-related hair loss have TSH levels within the reference range but suboptimal for follicle health. A full thyroid panel is essential.

Does stress cause hair loss?

Yes. Chronic stress elevates cortisol, which pushes follicles into the resting phase. The shedding typically appears two to three months after the stressful period. The good news is that stress-related hair loss (telogen effluvium) is almost always reversible once cortisol normalizes.

Can low iron cause hair loss even without anemia?

Yes. Ferritin can be low enough to cause hair loss well before you become anemic. Many specialists consider ferritin below 40 nanograms per milliliter insufficient for optimal hair growth, even though lab reference ranges may list normal as anything above 12. Supplementing iron when ferritin is low frequently produces noticeable regrowth within three to six months.

Is hormonal hair loss reversible?

In most cases, partially to fully reversible. Telogen effluvium from stress, thyroid dysfunction, iron deficiency, or postpartum shifts is almost always reversible. Androgenetic alopecia from DHT can be slowed and partially reversed with finasteride and minoxidil, especially when caught early. Women with PCOS or menopausal hair loss often see improvement with appropriate hormone management.