Hair Loss
Hair shedding and thinning have many causes — genetics, iron deficiency, stress, hormonal changes — and thyroid dysfunction is one recognised contributor.
Thyroid-related hair loss typically causes diffuse shedding rather than the patterned baldness of androgenetic alopecia.
Last medically reviewed: 1 November 2025
How thyroid affects hair
Both hypothyroidism and hyperthyroidism can trigger telogen effluvium — a temporary shift of hairs into the shedding phase. Hair typically thins diffusely over the scalp rather than receding at the temples.
Severe hypothyroidism may also cause brittle, dry hair and loss of the outer third of the eyebrows.
The timing issue
Telogen effluvium lags the trigger by 2–3 months — hair shedding noticed today may reflect thyroid dysfunction from months ago. Conversely, hair regrowth after treatment also takes months.
This delay is why hair loss alone is a weak indicator of current thyroid status.
Other causes to consider
Iron deficiency (ferritin), vitamin D deficiency, androgenetic alopecia, alopecia areata, postpartum hair loss, stress, rapid weight change, and certain medications all cause hair loss.
A comprehensive evaluation includes thyroid tests plus ferritin, and possibly other tests depending on the pattern.
Frequently asked questions
Will my hair grow back after thyroid treatment?
Usually yes — hair typically regrows over 6–12 months after thyroid function normalises, though full density may take longer.
Is eyebrow thinning specific to thyroid?
Loss of the outer third of the eyebrows is classically associated with hypothyroidism, though it is not specific and can occur with other conditions.
Should I take biotin for thyroid-related hair loss?
Biotin can interfere with some thyroid and other lab tests — always tell your doctor about supplements before testing.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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