Both hypothyroidism (underactive) and hyperthyroidism (overactive) can cause telogen effluvium — a diffuse, all-over thinning rather than a receding hairline. Thyroid hormone is needed for the hair-growth cycle, so when it's off, more hairs shed and regrowth slows. It often comes with other clues: fatigue, weight or temperature changes, dry skin or palpitations.
The good news is it's checkable and treatable: a simple TSH (and sometimes T4) blood test can flag it, and treating the thyroid usually lets hair recover over several months — though it can lag the blood numbers. Thyroid shedding can also overlap with pattern loss, so if thinning is concentrated at the crown or hairline, you may have both. Ask your doctor for thyroid tests if shedding is diffuse and unexplained.
Try the free self-check →Sources: AGA review (CCID) ↗
FAQ
Which thyroid test should I ask for?
Start with TSH; your doctor may add free T4 and thyroid antibodies. These flag both under- and overactive thyroid, the two patterns that cause shedding.
Does thyroid hair loss grow back?
Usually, once the thyroid is treated and stable — though regrowth can take several months and may lag behind your normalised blood tests.
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⚠️ When to see a doctor — don’t self-treat
- Sudden patchy or circular bald spots
- Redness, scaling, pus, pain or itch (possible scarring alopecia — treat urgently)
- Broken hairs or rapid loss
- Loss with body-wide signs (weight loss, fatigue, cycle changes, acne, extra hair)
- Loss right after a new medication
- Any hair loss in a child