Hair loss is one of the most distressing thyroid symptoms. The good news is that thyroid-related hair loss is usually temporary and improves once thyroid function is corrected — though regrowth takes time.
How thyroid disease affects hair
Hair growth cycles through phases: growth, transition and rest. Thyroid hormone helps regulate this cycle. When thyroid levels are abnormal, more hairs enter the resting phase and are shed.
Both an underactive and an overactive thyroid can cause diffuse thinning. The pattern is usually generalised rather than patchy.
What it looks like
Thyroid-related hair loss typically causes:
- Diffuse thinning over the whole scalp
- Increased shedding when washing or brushing
- Dry, coarse or brittle hair in hypothyroidism
- Fine, soft hair in some people with hyperthyroidism
It is different from patchy hair loss (alopecia areata) or scarring hair loss, which have other causes.
Other causes of hair loss
Hair loss is common and often multifactorial. Other causes include:
- Iron deficiency
- Postpartum hormonal changes
- Menopause
- Stress or illness (telogen effluvium)
- Certain medications
- Genetic pattern hair loss
- Skin conditions such as psoriasis or seborrhoeic dermatitis
A clinician may check iron, vitamin D and other factors alongside thyroid function.
How long does regrowth take?
Hair grows slowly — roughly one centimetre per month. After thyroid function normalises, shedding usually settles within a few months, and visible regrowth may take six to twelve months.
It is important to be patient and not to expect immediate change.
What helps
- Treat the thyroid condition and monitor levels.
- Correct iron or vitamin deficiencies if present.
- Eat enough protein and calories.
- Avoid harsh treatments, tight hairstyles and excessive heat.
- Use gentle hair care and a wide-toothed comb.
When to seek help
See a clinician if hair loss is patchy, accompanied by scalp redness or scaling, or persists despite normal thyroid function. Sudden severe shedding should also be assessed.
The bottom line
Thyroid-related hair loss is usually diffuse and reversible, but recovery takes months. Treating the thyroid is the foundation; patience and attention to other contributors help the process along.