Hair loss is one of the most common — and often overlooked — symptoms of thyroid disease. While many people associate thyroid problems with fatigue, weight changes, or low mood, the hair follicle is actually one of the most metabolically active structures in the body and is highly sensitive to thyroid hormones.
As a consultant dermatologist specializing in hair disorders, thyroid dysfunction is one of the primary medical causes I investigate when assessing patients with diffuse hair shedding or unexplained thinning.
The reassuring news is that thyroid-related hair loss is often reversible once the underlying hormonal imbalance is identified and treated.
How Does the Thyroid Affect Hair?
The thyroid gland produces hormones that regulate metabolism and energy use. Hair follicles depend on optimal thyroid hormone levels to maintain a healthy growth cycle. When these levels fluctuate, the hair cycle is disrupted, often leading to a condition called Telogen Effluvium, where hair enters the shedding phase prematurely.
Both:
- underactive thyroid disease (hypothyroidism)
and - overactive thyroid disease (hyperthyroidism)
can cause hair loss.
What Does Thyroid-Related Hair Loss Look Like?
Many patients ask, “What does thyroid hair loss look like?” Unlike Female Pattern Hair Loss, which usually causes thinning along the part line, thyroid-related shedding is typically diffuse (occurring evenly across the entire scalp).
Patients may notice:
- increased shedding in the shower or hairbrush
- reduced hair volume
- dry or brittle hair
- hair that feels finer or weaker
- slower hair growth
- thinning of the eyebrows, particularly the outer third
Unlike female pattern hair loss, thyroid-related shedding is usually more generalised across the scalp.
Thyroid Disease Is Common in Women
Thyroid dysfunction is much more common in women, particularly during midlife and after menopause.
Importantly, symptoms of thyroid disease often overlap with menopausal symptoms, including:
- fatigue
- low mood
- dry skin
- weight change
- hair thinning
This means thyroid disease may sometimes be missed in women presenting with “menopausal hair loss.”
In our Oxford University study published in the British Journal of Dermatology, we found that diffuse hair thinning becomes increasingly common after menopause and likely reflects a combination of hormonal and ageing-related mechanisms.
However, sudden or dramatic shedding is often a clue that another medical trigger — such as thyroid dysfunction — may also be contributing.
Can Thyroid Disease Cause Sudden Hair Shedding?
Yes.
Thyroid disease commonly triggers a condition called telogen effluvium, where more hairs than usual shift into the shedding phase of the hair cycle.
This can lead to:
- sudden excessive shedding
- hair coming out in large amounts during washing
- noticeable reduction in density over weeks or months
Importantly, hair loss often appears several months after thyroid hormone levels first become abnormal because of the delayed nature of the hair cycle.
What Blood Tests Are Important?
When assessing diffuse hair loss, thyroid testing is often an important part of the investigation.
Tests may include:
- TSH (thyroid stimulating hormone)
- free T4
- thyroid antibodies (in selected cases)
Other useful blood tests often include:
- ferritin (iron stores)
- vitamin D
- B12
- zinc (in selected cases)
Iron deficiency and vitamin deficiencies can coexist with thyroid disease and may worsen shedding.
Can Hair Grow Back After Thyroid Treatment?
In many cases, yes.
Once thyroid hormone levels are stabilised, excessive shedding often improves gradually over several months. Hair regrowth can take time because the hair cycle recovers slowly.
However, recovery may be slower if:
- thyroid disease has been untreated for a long time
- nutritional deficiencies are present
- female pattern hair loss also coexists
- there is underlying inflammatory scalp disease
When Should You Seek Help?
It is sensible to seek medical assessment if you notice:
- sudden excessive hair shedding
- diffuse thinning across the scalp
- eyebrow thinning
- dry, brittle hair
- persistent shedding lasting more than 3–6 months
- hair loss associated with fatigue or weight change
Hair loss is not always simply “stress” or “normal ageing.” Identifying underlying medical causes such as thyroid dysfunction is important because many are treatable.
Final Thoughts
The thyroid gland plays an important role in maintaining healthy hair growth. When thyroid hormone levels become abnormal, diffuse shedding and hair quality changes are common.
Because thyroid disease frequently overlaps with menopause and other causes of hair thinning, careful assessment is important.
The good news is that thyroid-related hair loss is often reversible with appropriate diagnosis, treatment and optimisation of overall hair and scalp health.
