Thyroid-Related Hair Changes
Beyond simple shedding, thyroid dysfunction can cause several distinct hair changes — dryness, brittleness, slow growth, and eyebrow thinning.
These changes reflect the hormone’s role in the hair growth cycle and skin health.
Last medically reviewed: 1 November 2025
Types of changes
Hypothyroidism typically causes dry, coarse, brittle hair that breaks easily, slowed growth, diffuse thinning, and loss of the outer third of the eyebrows. Hyperthyroidism can cause fine, soft hair and increased shedding.
These changes are part of a broader picture of dry skin, brittle nails and slowed metabolism.
Why eyebrows specifically?
Eyebrow thinning — particularly the lateral (outer) portion — is a classic but non-specific sign of hypothyroidism. It may relate to slower hair cycling in that region and has been recognised clinically for decades.
It is not diagnostic on its own but adds a small piece of evidence when combined with other features.
Resolution after treatment
Hair changes improve gradually over 6–12 months after thyroid function normalises. The hair growth cycle is slow, so patience is needed — regrowth is not immediate.
Persistent hair loss despite normal thyroid function warrants evaluation for other causes such as iron deficiency or androgenetic alopecia.
Frequently asked questions
Are thyroid hair changes permanent?
No — they typically reverse with adequate thyroid treatment over months, though complete recovery can take a year or more.
Does hyperthyroidism also affect hair?
Yes — it can cause increased shedding and fine, brittle hair, opposite in pattern to hypothyroidism. Both resolve with treatment.
What if my hair doesn’t recover after treatment?
Consider other causes — ferritin/iron, vitamin D, genetics, stress, or dermatological conditions. A dermatologist can assess if thyroid tests are normal.
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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