Thyroid problems and hair loss: signs to know

The thyroid is a small gland in the neck that makes hormones controlling how the body uses energy. When it makes too little or too much hormone, many body systems are affected, including the skin and hair. Thyroid problems are common, especially in women, and hair changes are sometimes one of the first things people notice ^{1 2}.

How thyroid hormones affect hair

Hair follicles go through a cycle of growth, rest and shedding. Thyroid hormones are among the signals that help regulate this cycle, and research has shown that they act directly on human hair follicles ³. When thyroid hormone levels are out of balance for some time, more hairs may move into the resting phase and then fall out, leading to diffuse shedding across the whole scalp rather than bald patches ⁴.

Underactive thyroid (hypothyroidism)

An underactive thyroid means the gland does not make enough hormone. Symptoms usually develop slowly and can include ¹:

• Tiredness and feeling slow
• Weight gain
• Feeling cold
• Dry skin and dry, coarse hair or hair loss
• Constipation
• Low mood
• Heavier or irregular periods

Some people notice thinning of the outer part of the eyebrows as well. Because these symptoms are common and develop gradually, they can easily be put down to stress or age.

Overactive thyroid (hyperthyroidism)

An overactive thyroid makes too much hormone. Symptoms can include ²:

• Feeling nervous, anxious or irritable
• Fast or irregular heartbeat
• Weight loss despite eating normally
• Feeling hot and sweating
• Shaky hands
• Difficulty sleeping
• Thinning hair or hair loss

Thyroid disease and other hair conditions

People with autoimmune thyroid disease have a higher chance of other autoimmune conditions, including alopecia areata, which causes round patches of hair loss ⁵. If you have patchy hair loss rather than general thinning, see alopecia areata. Thyroid problems can also occur at the same time as female or male pattern hair loss, so more than one cause may be involved.

Getting tested

Thyroid problems are diagnosed with a blood test, usually measuring thyroid-stimulating hormone (TSH) and thyroxine (T4) ¹. It is a simple test. If you have hair loss along with any of the symptoms above, ask a doctor whether a thyroid test is appropriate. Doctors often check iron levels and a full blood count at the same time, because low iron is another common cause of shedding ⁶. See anaemia and hair loss.

Treatment and what happens to hair

• Underactive thyroid is usually treated with daily levothyroxine tablets to replace the missing hormone, with blood tests to find the right dose ¹
• Overactive thyroid may be treated with medicines that reduce hormone production, radioactive iodine or, sometimes, surgery ²

When thyroid hormone levels are brought back to normal, hair shedding caused by the thyroid problem often settles. Be patient: because of the slow hair cycle, it can take several months before shedding reduces and new growth becomes visible ⁴. Some people notice a temporary increase in shedding around the time treatment starts or the dose changes, which usually settles.

If thinning continues once thyroid levels have been normal for some months, another cause such as pattern hair loss may be present, and it is worth getting the scalp checked again.

Things that do not help

• Taking thyroid medicine or "thyroid support" supplements without a diagnosis. Thyroid hormone should only be taken when prescribed. Too much can cause an overactive thyroid ²
• High-dose iodine or kelp supplements. These can upset thyroid function in some people. Most people get enough iodine from a balanced diet ⁷

Caring for your hair meanwhile

While treatment takes effect, be gentle with your hair ⁸:

• Use a mild shampoo and conditioner, especially if hair feels dry
• Avoid tight styles and harsh chemical treatments
• Lower the heat on styling tools

When to see a doctor

See a GP if you have hair loss with tiredness, weight change, feeling unusually hot or cold, a fast heartbeat or a swelling in the neck. Seek urgent help for a very fast or irregular heartbeat with chest pain or breathlessness.

The bottom line

Both an underactive and an overactive thyroid can cause diffuse hair shedding. A simple blood test can check thyroid function. Once levels are corrected, shedding often settles over several months. For a wider view of medical causes, read when hair loss can be a sign of illness.

Frequently asked questions

Can thyroid problems cause hair loss?

Yes. Both an underactive and an overactive thyroid can cause hair thinning or shedding, usually spread across the scalp ^{1 2}.

Will my hair grow back after thyroid treatment?

Shedding caused by a thyroid problem often settles once hormone levels are normal, but it can take several months because of the slow hair cycle ^{4 3}.

Can levothyroxine cause hair loss?

Some people notice temporary shedding when starting treatment or changing dose. Tell your doctor if hair loss continues, as the dose or another cause may need checking ¹.

Which blood test checks the thyroid?

Usually TSH and thyroxine (T4). A doctor may also check iron and a full blood count if you have hair loss ^{1 6}.

Educational content. Not medical advice.