Thyroid Hair Fall: How Your Gland Affects Your Hair

It starts with a few extra strands on the bathroom floor after your morning bath. Then you notice more hair on your pillow and in your comb. At first, you blame the weather or your shampoo. However, something else feels different too. You are tired by late afternoon, feel cold even when everyone else wants the fan on, and your skin seems unusually dry. Then, during a routine health check, your blood report shows an abnormal TSH level. Your doctor mentions a thyroid problem, and suddenly, you wonder whether it explains your hair loss. Thyroid hair fall happens when too little or too much thyroid hormone affects your normal hair growth cycle. According to the American Academy of Dermatology, thyroid disorders can cause noticeable hair thinning and shedding. The encouraging part is that hair often starts recovering once thyroid hormone levels are brought under control with treatment, although regrowth can take several months. So, how exactly does your thyroid affect your hair, what signs should you look for and what can you do to support healthy regrowth?

How does your thyroid affect hair growth?

Your thyroid is a small, butterfly-shaped gland at the front of your neck. It produces two important hormones, T3 and T4, which help regulate how your body uses energy and how its cells function. These hormones also play a role in keeping your hair healthy. Each strand of hair grows from a follicle beneath your scalp. Hair doesn't grow continuously, though. It follows a natural cycle with three main stages:

1. Growth phase (anagen): Hair actively grows, often for several years.

2. Transition phase (catagen): Growth slows, and the follicle prepares to rest.

3. Resting phase (telogen): Hair eventually sheds, making way for a new strand.

Thyroid hormones help regulate this cycle. A laboratory study on human scalp hair follicles found that thyroid hormone T4 supported hair growth by extending the growth phase and encouraging the activity of cells that form the hair shaft. However, both too little and too much thyroid hormone can disturb normal hair growth, leading to increased shedding or thinning. A review of hormones and hair loss also discusses links between thyroid disorders and several types of hair loss, including:

• Telogen effluvium: Increased shedding when more hairs enter the resting phase.

• Alopecia areata: Patchy hair loss associated with an autoimmune condition.

• Pattern hair loss: Gradual thinning, often around the parting or crown.

These conditions have different causes, and thyroid problems don't necessarily cause all of them. However, thyroid function is one factor doctors may consider when investigating unexplained hair loss.

Hypothyroidism and hyperthyroidism: what each does to hair

When the thyroid is underactive

Hypothyroidism means the gland makes too little hormone. Body processes slow down. MedlinePlus lists dry, thinning hair among its symptoms, along with tiredness, weight gain, feeling cold, constipation, dry skin and heavy or irregular periods. Because hypothyroidism develops slowly, the NIDDK notes that you may not notice symptoms for months or even years.

When the thyroid is overactive

Hyperthyroidism means too much hormone. Many body processes speed up. As the follicle study above notes, excess thyroid hormone can also cause shedding.

Why the hair fall can appear late

Thyroid hair fall can show up some time after the hormone change began. Hairs that are pushed into the resting phase stay on the scalp for a while before they fall. If your hair fall seems to change soon after you start treatment, keep taking your medicine and tell your doctor rather than stopping it.

Will your hair grow back after thyroid treatment?

Hair often grows back with treatment. The American Academy of Dermatology says that treating the thyroid disease can reverse the hair loss. The same page notes that some people with a thyroid problem see their hair come out in clumps when they brush it, which can be frightening to watch. Knowing that regrowth is possible makes the waiting easier. Hair grows slowly, so it can take months after your levels settle before the parting looks fuller. If your thyroid levels are normal on treatment and the hair is still thinning months later, there may be a second cause. Low iron, pattern hair loss, a recent illness or crash dieting can all overlap with a thyroid problem. That is a reason to see a dermatologist, not to change your thyroid dose yourself.

Which tests should you ask for?

A diagnosis cannot be made from symptoms alone. The NIDDK explains that tiredness and weight gain are common and do not necessarily mean a thyroid problem. Blood tests are used to find out. NIDDK lists the thyroid blood tests as TSH, T4, T3 and thyroid antibody tests:

• TSH (thyroid stimulating hormone) is usually checked first. A high TSH most often means an underactive thyroid. A low TSH usually means an overactive one.

• T4 and T3 help find the cause when TSH is not normal.

• Thyroid antibodies may help diagnose an autoimmune cause such as Hashimoto's disease.

The AAD notes that too little iron can cause hair loss of its own, so ask your doctor whether an iron check makes sense too. Tell your doctor about every supplement you take before a thyroid test. In a small study, 13 adults took a high dose of 10 mg a day. The biotin interfered with some thyroid blood tests, depending on the lab machine used. Your doctor may ask you to pause any biotin supplement before the sample is taken. If your report shows low iron as well, read this article on iron deficiency in women, which explains what ferritin means and how it is corrected.

Living with thyroid medicine

For hypothyroidism, the usual treatment is a daily tablet of levothyroxine, a man-made copy of the hormone. MedlinePlus advises taking iron or calcium supplements at least four hours before or after levothyroxine, because they can reduce how much of the medicine you absorb. The NIDDK notes that your doctor may recommend taking the medicine in the morning before eating. A few practical habits can help:

1. Take your tablet at the same time every day.

2. Keep your morning chai or coffee a little after the tablet, as your doctor advises.

3. Do not stop or change the dose because your hair looks better or worse. Hair is a slow signal.

4. Repeat your blood test when your doctor asks. Doses are adjusted based on the numbers.

How to support hair regrowth while treating thyroid problems

Getting your thyroid hormone levels back into a healthy range is the most important step in managing thyroid-related hair fall. While treatment addresses the underlying cause, a balanced diet and gentle hair care can help support healthy hair regrowth. The American Academy of Dermatology (AAD) notes that deficiencies in nutrients such as iron, protein, zinc and biotin can also contribute to hair loss. Here are a few habits worth following:

1. Include protein in every meal. Foods such as dal, curd, paneer, eggs, fish and chicken provide the protein your body needs to produce hair.

2. Eat iron-rich foods. Include leafy greens, ragi, sprouts, legumes and meat where appropriate. Pair plant-based iron sources with vitamin C-rich foods to improve absorption.

3. Get enough zinc. Nuts, seeds, whole grains and legumes are useful everyday sources of this mineral, which supports normal hair growth.

4. Use iodised salt in moderation. Iodine is essential for thyroid hormone production, but taking extra iodine isn't always helpful and may worsen certain thyroid conditions. Follow your doctor's advice.

5. Choose gentle hair care. Use a mild shampoo, apply conditioner after washing and avoid hairstyles that pull tightly on your roots.

Small changes to how you handle your hair can also reduce breakage. Pat it dry with a soft towel instead of rubbing, detangle gently with a wide-tooth comb and limit frequent straightening or blow-drying at high temperatures. Remember that these habits support hair health, but they cannot replace thyroid treatment. Hair regrowth takes time, and taking extra supplements without a confirmed deficiency won't necessarily make it happen faster.

When to see a doctor about hair fall

It is worth seeing your doctor or an endocrinologist if:

• you have hair fall along with other symptoms MedlinePlus lists for an underactive thyroid, such as tiredness, weight gain, feeling cold or heavy or irregular periods

• you have a family history of thyroid disease or were pregnant in the past 6 months, which NIDDK lists among things that make an underactive thyroid more likely

• you are on thyroid medicine and develop chest pain or a rapid heartbeat, your symptoms get worse or do not improve, or you develop new symptoms, which MedlinePlus lists as reasons to contact your doctor

• you are pregnant or planning a pregnancy and have a thyroid condition. NIDDK says untreated hypothyroidism in pregnancy can affect both mother and baby

See a dermatologist if hair fall continues after your thyroid levels are normal or you are worried about it. Our guides on hair loss in women and hair shedding vs hair breakage can help you describe what you are seeing.

Thyroid hair fall: Recovery takes time

Thyroid-related hair fall can be worrying, but it is often reversible with proper treatment. Take your prescribed medication, monitor your thyroid levels and maintain a balanced diet. Hair regrowth takes time, so be patient with the process. As your thyroid levels stabilise, your hair may gradually regain its fullness.

Sources

• Thyroid hormones directly alter human hair follicle functions (J Clin Endocrinol Metab, 2008)

• The hormonal background of hair loss in non-scarring alopecias (Biomedicines, 2024)

• Hypothyroidism (MedlinePlus)

• Hypothyroidism (NIDDK)

• Hair loss: 18 causes (American Academy of Dermatology)

• Biotin interference in assays for thyroid hormones, thyrotropin and thyroglobulin (Thyroid, 2021)

• Levothyroxine (MedlinePlus)

Medical Disclaimer: This article is for general information and is not a substitute for advice from your doctor. Speak to a qualified healthcare professional before starting any supplement, especially if you are pregnant, breastfeeding or taking medication.