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Illness · Updated 2026-10-30 · Editorial review in progress
Thyroid hair loss: the regrowth timeline after diagnosis
Also searched as: hypothyroidism hair loss regrowthhyperthyroidism hair lossHashimoto's hair lossthyroid hair loss grow back
Severe and prolonged hypothyroidism or hyperthyroidism can cause diffuse hair loss; regrowth is usual with successful treatment but takes several months and may be incomplete, and because of the long hair cycle the shedding can appear after treatment starts (British Thyroid Foundation).
No consistent week-by-week window is published for this, so it is not on the calculator.
The timeline
| Stage | When (typically) | What's happening |
|---|---|---|
| Appears | Several months after the thyroid problem began | BTF: hair loss becomes apparent several months after onset of thyroid disease, due to the long hair cycle. [British] |
| The paradox | Can coincide with starting treatment | BTF: hair loss may follow treatment and the medication may be wrongly blamed. [British] |
| Regrowth | Several months; may be incomplete | BTF: regrowth is usual with successful treatment, though it takes several months. [British] |
Who this usually happens to
| Situation | What BTF says |
|---|---|
| Severe, prolonged under- or overactive thyroid | Can cause diffuse loss over the whole scalp [British] |
| Mild or subclinical thyroid problems | Unusual to cause hair loss [British] |
| Short-lived thyroid problems | Unusual to cause hair loss [British] |
| Radioiodine treatment | Does not cause hair loss [British] |
Why stopping thyroid medicine backfires
BTF warns that blaming the medication can lead to stopping it, which in turn may worsen the hair loss [British]. If your shedding started after diagnosis, the more likely culprit is the months the thyroid was off before treatment.
Normal vs. warning signs
- Even thinning over the whole scalp
- Shedding in the first months after starting treatment
- New hair with a slightly different texture
- Patches or smooth bald spots
- Scalp pain, redness, burning or scaling
- Loss of eyebrows, eyelashes or body hair
- Thinning in a pattern at the crown or part that keeps progressing once levels are stable
What may help
- Keep taking thyroid medication as prescribed and keep your blood-test schedule.
- Ask whether iron or other levels should be checked too.
- Judge regrowth in months, with photos, not day to day.
Related triggers
Levothyroxine changes
MedicationsMethimazole & carbimazole (antithyroid drugs)
Labs & explainersFerritin & iron
Life eventsPostpartum
Frequently asked questions
Will hair grow back after thyroid treatment?
Usually, but it takes several months and may be incomplete, per the British Thyroid Foundation.
Why is my hair falling out after starting levothyroxine?
BTF explains the loss may simply appear after treatment starts because of the long hair cycle, so the medicine gets wrongly blamed.
Does mild hypothyroidism cause hair loss?
BTF says it is unusual for mild (subclinical) or short-lived thyroid problems to cause hair loss.
Does radioactive iodine cause hair loss?
No — the British Thyroid Foundation states radioiodine does not cause hair loss.
Sources
- British Thyroid Foundation. Hair loss and thyroid disorders
- DermNet (Chang F-L, Oakley A, 2019). Telogen effluvium
- American Academy of Dermatology. Do you have hair loss or hair shedding?