Thyroid and Hair Loss: Can a Thyroid Problem Cause Hair Loss?
Last reviewed on 3 August 2026. We review our treatment guides every six months to keep them accurate.
Thyroid and hair loss are closely linked. Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can cause the hair to thin. The reassuring part is that this kind of hair loss is usually temporary: once the thyroid problem is diagnosed and treated, and hormone levels settle, the hair generally grows back, although it can take several months.
This guide explains how thyroid hormones affect the hair cycle, what thyroid-related shedding looks like, and what usually helps. It is general information, not a diagnosis. For authoritative guidance, see the NHS pages on underactive thyroid and overactive thyroid, and the British Thyroid Foundation. If you are worried about your hair or your thyroid, speak to your GP.
How your thyroid affects the hair cycle
The thyroid is a small gland in the front of the neck. It makes hormones, mainly thyroxine (T4) and triiodothyronine (T3), that control how the body uses energy. These same hormones help regulate the hair growth cycle.
Each hair follicle moves through a long growth phase and then a resting phase, called telogen, at the end of which the hair is shed and replaced. When thyroid hormone levels stay too high or too low, more follicles than usual are pushed into the resting phase at the same time. Several weeks later they shed together, a pattern doctors call telogen effluvium. Because the hair cycle is slow, the shedding often only becomes noticeable months after the thyroid problem began. You can read more in our guide to telogen effluvium.
What thyroid hair loss looks like
Thyroid-related hair loss is usually diffuse. The British Thyroid Foundation explains that the loss involves the whole scalp rather than distinct bald spots, so the hair looks evenly thinner all over. This is different from the patchy, coin-shaped bald areas of alopecia areata, which is a separate condition covered below.
Other changes people sometimes notice include:
- Hair that feels drier, coarser or more brittle, which is more common with an underactive thyroid
- Finer, softer hair that breaks easily, sometimes seen with an overactive thyroid
- Thinning of the outer edge of the eyebrows, which can occur with an underactive thyroid
Mild or short-lived thyroid problems do not usually cause noticeable hair loss, and it is unusual for a thyroid problem to affect the hair without other symptoms such as tiredness, weight change, or feeling too hot or too cold. If you have diffuse shedding on its own, your doctor may look for other common causes, such as iron deficiency or general diffuse thinning.
Underactive thyroid (hypothyroidism)
An underactive thyroid does not make enough thyroid hormone. The NHS lists dry skin, dry hair or hair loss among its symptoms, alongside tiredness, weight gain, feeling cold and low mood. In the UK the most common cause is Hashimoto's disease, an autoimmune condition. It is usually treated with a daily hormone-replacement tablet called levothyroxine.
Overactive thyroid (hyperthyroidism)
An overactive thyroid makes too much thyroid hormone. The NHS lists hair thinning among its signs, along with weight loss, a fast or irregular heartbeat, feeling anxious, sweating and sensitivity to heat. A common cause is Graves' disease which, like Hashimoto's, is autoimmune.
The autoimmune link and alopecia areata
Most people with an under- or overactive thyroid have an autoimmune form of thyroid disease. Having one autoimmune condition makes another slightly more likely. One example is alopecia areata, in which the immune system attacks the hair follicles and causes discrete, often circular, bald patches. The British Thyroid Foundation notes that alopecia areata occurs in people with autoimmune thyroid disease more often than would be expected by chance. It is different from the even, all-over thinning caused directly by thyroid hormone changes. Our guide to alopecia areata explains it in more detail.
Can thyroid hair loss be reversed?
Usually, yes. The British Thyroid Foundation explains that regrowth is normal once the thyroid disorder is treated successfully, although it can take several months and may be incomplete. Because the hair cycle is slow, recovery lags behind your blood tests: your thyroid levels may return to normal well before you see new hair. New hair sometimes comes back with a slightly different texture or colour. Patience helps, as does handling the hair gently while it recovers.
Levothyroxine and shedding
Some people notice shedding in the early months of treatment, and the NHS lists hair loss as a possible side effect of levothyroxine. This is usually temporary and often settles as the dose is adjusted. It can be hard to tell whether early shedding comes from the medicine or from the underlying thyroid problem that started months earlier. Either way, it is not a reason to stop treatment on your own. The NHS advises continuing the medicine unless a doctor tells you otherwise, so speak to your GP or pharmacist if you are concerned.
How thyroid problems are diagnosed
A thyroid problem is diagnosed with a simple blood test arranged by your GP, which measures thyroid-stimulating hormone (TSH) and thyroxine (T4). If your hair loss might be linked to your thyroid, your GP can check this and look for other common causes at the same time. Sometimes a referral to a dermatologist, a skin and hair specialist, is helpful if the picture is unclear.
When to see your GP
See your GP if your hair loss is worrying you, if it comes with other symptoms of a thyroid problem, or if it does not improve once your thyroid is treated and stable. If the hair does not fully recover, a dermatologist can check whether another type of hair loss is also present. Be cautious with supplements marketed for hair or for "thyroid support", as some contain iodine or biotin that can interfere with thyroid tests or treatment.
Frequently asked questions
Can a thyroid problem cause hair loss?
Yes. Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can make the hair thin, usually as diffuse shedding across the whole scalp rather than in patches. It tends to happen when the thyroid problem is more marked or has been present for a while.
Can hypothyroidism cause hair loss?
Yes. The NHS lists hair loss among the symptoms of an underactive thyroid, often alongside dry skin and dry hair. Treating the underactive thyroid with levothyroxine usually allows the hair to recover over several months.
Can hyperthyroidism cause hair loss?
Yes. An overactive thyroid can cause the hair to become fine and to thin. As with an underactive thyroid, the hair generally recovers once thyroid hormone levels are brought back to normal.
How long does thyroid hair loss take to grow back?
Regrowth usually begins once thyroid levels are stable, but it lags behind your blood tests and often takes several months to become visible. There is no fixed before-and-after timeline, as recovery varies from person to person and can be incomplete. Gentle hair care while you wait is sensible.
Is thyroid hair loss permanent?
It is usually temporary. Most thyroid-related hair loss improves once the thyroid is treated and hormone levels are stable. If your hair does not fully recover, see your GP or a dermatologist, as another cause may be involved.
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