Thyroid-Related Hair Loss: How Hypothyroidism and Hyperthyroidism Cause Hair Thinning

Hair loss is one of the most distressing and commonly overlooked symptoms of thyroid dysfunction. While many people associate thyroid disease with fatigue, weight changes, or mood swings, the impact on hair health — particularly hair thinning and shedding — is just as significant. Both hypothyroidism (an underactive thyroid) and hyperthyroidism (an overactive thyroid) can trigger noticeable, sometimes severe, hair loss. Understanding the connection between your thyroid gland and your hair follicles is the first step toward regaining thick, healthy hair.

What Is the Thyroid and Why Does It Matter for Hair?

The thyroid is a small, butterfly-shaped gland located at the base of your neck. It produces two primary hormones — triiodothyronine (T3) and thyroxine (T4) — that regulate your body's metabolism. These hormones influence everything from heart rate and energy levels to body temperature and, crucially, the growth cycle of your hair.

Hair follicles are among the most metabolically active tissues in the body. They depend on a steady, well-regulated supply of thyroid hormones to sustain their rapid cell division and normal growth phases. When thyroid hormone levels fall out of balance — whether too high or too low — hair follicles are among the first to feel the disruption.

Hypothyroidism and Hair Loss: When the Thyroid Is Underactive

Hypothyroidism occurs when the thyroid gland does not produce enough T3 and T4. It is one of the most prevalent endocrine disorders worldwide, affecting women far more commonly than men — particularly those over the age of 35. Hashimoto's thyroiditis, an autoimmune condition, is the leading cause of hypothyroidism.

When thyroid hormones are insufficient, the body's metabolic processes slow down. This slowdown extends to the hair follicle cycle. Normally, hair passes through three stages: the anagen (growth) phase, the catagen (transition) phase, and the telogen (resting/shedding) phase. In hypothyroidism, follicles are prematurely pushed out of the growth phase and into the resting phase — a process known as telogen effluvium. The result is diffuse hair thinning across the entire scalp rather than patchy bald spots.

One of the hallmark signs of hypothyroid-related hair loss is the thinning of the outer third of the eyebrows, often referred to as "Queen Anne's sign." Hair across the scalp tends to become dry, brittle, coarse, and slow-growing before it begins to shed. Because the process is gradual, many people don't realise the connection until they've already lost a significant amount of volume.

Beyond the scalp, hypothyroidism can also lead to loss of body hair, including leg and arm hair, eyelashes, and pubic hair. The skin often becomes dry and flaky simultaneously, as the sebaceous glands — like the hair follicles — are also affected by low thyroid hormone levels.

Hyperthyroidism and Hair Loss: When the Thyroid Is Overactive

Hyperthyroidism presents the opposite problem: the thyroid produces an excess of hormones, accelerating the body's metabolic processes. Graves' disease, an autoimmune disorder, is the most common cause. Other causes include toxic multinodular goitre and thyroiditis.

Paradoxically, both too little and too much thyroid hormone cause hair loss, though through slightly different mechanisms. In hyperthyroidism, the hair growth cycle is accelerated to the point of exhaustion. Hair follicles cycle through their growth and shedding phases far too quickly, leading to a rapid depletion of actively growing hairs. The result, again, is diffuse hair thinning — often accompanied by fine, soft hair texture and excessive shedding.

In hyperthyroidism, hair loss tends to be more sudden and dramatic than in hypothyroidism. Patients often notice large amounts of hair coming out in the shower, on pillows, or in hairbrushes. The hair may look and feel finer than usual before the thinning becomes visually apparent. Some people with Graves' disease also develop a condition called alopecia areata — patchy hair loss — as both conditions share an autoimmune origin.

Additionally, hyperthyroidism-related hair loss is sometimes complicated by the medications used to treat the condition. Certain anti-thyroid drugs, including carbimazole and propylthiouracil, have hair loss listed as a potential side effect, making it difficult to distinguish drug-induced shedding from disease-related shedding.

Why Women Are Disproportionately Affected

Thyroid disorders affect women approximately five to eight times more often than men, making thyroid-related hair loss a particularly significant concern for female patients. The reasons are multifactorial. Women are more prone to autoimmune conditions in general, and the hormonal fluctuations that accompany puberty, pregnancy, postpartum recovery, and menopause create additional vulnerability windows for thyroid dysregulation.

Postpartum thyroiditis, for example, affects up to 10% of women after childbirth. It often triggers a temporary phase of hyperthyroidism followed by hypothyroidism — both of which can cause hair loss — in the months following delivery. This is frequently mistaken for postpartum hair shedding, a normal hormonal occurrence, and may go undiagnosed as a thyroid issue.

The emotional toll of hair loss in women cannot be understated. For many, hair is deeply tied to identity, confidence, and femininity. Discovering that a medical condition is causing thinning hair can be distressing, but identifying the root cause is also empowering — because thyroid-related hair loss is often reversible with proper treatment.

Diagnosing the Connection: What to Look For

Thyroid-related hair loss rarely occurs in isolation. It typically accompanies other symptoms of thyroid dysfunction. In hypothyroidism, you may notice persistent fatigue, unexplained weight gain, cold intolerance, constipation, brain fog, dry skin, a slow heart rate, and depression. In hyperthyroidism, symptoms often include unintentional weight loss, heart palpitations, anxiety, excessive sweating, heat intolerance, diarrhoea, tremors, and difficulty sleeping.

If you are experiencing hair loss alongside any of these symptoms, it is important to consult a doctor and request a thyroid function test. This typically involves a blood test measuring TSH (thyroid-stimulating hormone) levels, along with free T3 and free T4 levels where indicated. An elevated TSH points toward hypothyroidism; a suppressed TSH suggests hyperthyroidism. Antibody tests, such as TPO antibodies (for Hashimoto's) and TSI or TRAb antibodies (for Graves' disease), help identify the underlying autoimmune cause.

It is worth noting that hair loss can sometimes occur even when thyroid levels fall within the "normal" reference range — particularly in individuals with Hashimoto's whose levels fluctuate. A conversation with an endocrinologist or a thyroid-specialist doctor is essential if symptoms persist despite normal basic TSH results.

Treatment: Can Thyroid-Related Hair Loss Be Reversed?

The good news is that in most cases, thyroid-related hair loss is reversible once the underlying hormonal imbalance is treated and stabilised.

For hypothyroidism, the standard treatment is daily oral levothyroxine — a synthetic form of T4. Once thyroid hormone levels are optimised, hair follicles gradually return to their normal growth cycle. However, regrowth is not immediate; it can take anywhere from three to six months to see a meaningful improvement, and full recovery may take up to a year or longer depending on the severity and duration of the deficiency.

For hyperthyroidism, treatment options include anti-thyroid medications (methimazole or propylthiouracil), radioiodine therapy, or thyroid surgery. Once hormone levels are brought back within the normal range, hair shedding typically slows and regrowth begins. In cases where medication is the cause of continued shedding, a doctor may adjust the dosage or explore alternative treatments.

It is important not to self-medicate with thyroid supplements, iodine, or herbal remedies without medical supervision. Overuse of iodine, in particular, can worsen both hypothyroidism and hyperthyroidism and further damage hair health.

Supporting Hair Recovery During Thyroid Treatment

While medical treatment addresses the root cause, there are complementary steps you can take to support hair health during recovery. Nutritional deficiencies — especially of iron, ferritin, zinc, biotin, and vitamin D — often coexist with thyroid disorders and independently contribute to hair loss. A full nutrient panel is a valuable add-on to thyroid testing, and supplementing any identified deficiencies under medical guidance can accelerate hair recovery.

Gentle hair care practices also make a meaningful difference during this vulnerable period. Avoid heat styling, harsh chemical treatments, tight hairstyles, and excessive brushing. Use a nourishing, sulphate-free shampoo formulated for thinning hair, and consider incorporating a scalp-stimulating hair serum or treatment that supports follicle health and circulation.

Stress management is equally important, as chronic stress elevates cortisol levels, which can suppress thyroid function and independently trigger telogen effluvium — creating a vicious cycle of hair loss. Prioritising sleep, light exercise, and mindfulness practices supports both thyroid health and hair recovery.

When to Seek Further Help

If hair loss continues significantly despite optimised thyroid levels, it may be worth exploring other contributing factors such as iron deficiency anaemia, polycystic ovary syndrome (PCOS), or androgenetic alopecia. A dermatologist specialising in hair and scalp disorders, or a trichologist, can perform a detailed scalp analysis to identify whether other conditions are at play.

In some cases, adjunctive treatments such as minoxidil (topical or oral) may be recommended to support regrowth while the underlying condition is managed. Platelet-rich plasma (PRP) therapy is another emerging option showing promise for individuals with thyroid-related hair thinning who are seeking to accelerate recovery.

Final Thoughts

Thyroid-related hair loss is far more common than it is talked about, and it is frequently the symptom that first prompts people to seek medical attention — and rightfully so. Whether caused by an underactive or overactive thyroid, the hair loss follows a similar pattern of diffuse thinning across the scalp, often accompanied by changes in hair texture and growth rate. Women are significantly more affected than men, and many cases go undiagnosed for months or even years.

The key message is this: if you are experiencing unexplained hair thinning, do not dismiss it as simple stress or ageing without ruling out a thyroid issue. A straightforward blood test can provide answers and, more importantly, a clear path toward treatment. With the right medical care, nutritional support, and gentle hair practices, the majority of people with thyroid-related hair loss can expect meaningful — and often complete — recovery of their hair.