Thyroid disorders are among the most commonly missed causes of hair loss, particularly in women. Both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) can cause significant hair shedding. The good news: once thyroid function is corrected, hair loss typically reverses.
How the Thyroid Affects Hair
The thyroid gland produces hormones (T3 and T4) that regulate metabolic rate throughout the body, including in hair follicles. Hair follicles are among the most metabolically active structures in the body — they are sensitive to any disruption in thyroid hormone levels.
Both too little and too much thyroid hormone can push follicles into the resting (telogen) phase prematurely, resulting in increased shedding (telogen effluvium). The diffuse, all-over nature of this shedding is characteristic — unlike androgenetic alopecia, which follows a pattern.
Hypothyroidism and Hair Loss
Hypothyroidism (underactive thyroid) is more commonly associated with hair loss. Typical features include:
- Diffuse thinning across the entire scalp (not following a pattern)
- Hair becoming dry, coarse, and brittle
- Loss of the outer third of the eyebrows (a classic but not universal sign)
- General fatigue, weight gain, cold intolerance, depression (associated symptoms)
The cause is usually autoimmune (Hashimoto's thyroiditis) or post-radioactive iodine treatment.
Hyperthyroidism and Hair Loss
Hyperthyroidism (overactive thyroid) can also cause diffuse hair shedding, though this is less commonly recognised. Associated symptoms include weight loss, palpitations, heat intolerance, and anxiety.
Diagnosis
A simple blood test measuring TSH (thyroid stimulating hormone) is the initial screening test. Abnormal TSH levels prompt further testing of T3, T4, and thyroid antibodies. Any patient with unexplained diffuse hair loss should have thyroid function checked.
Treatment
Treatment of the underlying thyroid disorder typically reverses the hair loss over 3–6 months as thyroid hormone levels normalise. Hair may not return immediately — there is typically a lag of several months between normalising thyroid function and seeing hair recovery.
If hair loss persists after thyroid function has been corrected for 6+ months, other causes should be assessed — including nutritional deficiencies (iron, ferritin, vitamin D) that often co-occur with thyroid disease, or co-existing androgenetic alopecia.
Is Hair Transplant Appropriate for Thyroid-Related Hair Loss?
In general, hair transplantation is not appropriate for hair loss caused by thyroid dysfunction. The loss is diffuse rather than patterned, and transplanting into areas of diffuse loss produces poor results. Moreover, once thyroid function is corrected, the hair typically recovers without transplantation.
Transplant may be considered in patients who have persistent patterned hair loss after thyroid function has been fully corrected for at least 12 months, and where the residual loss pattern is clearly androgenetic rather than diffuse.
Experiencing diffuse hair loss and unsure of the cause? Our team can advise on assessment pathways and discuss whether transplantation is appropriate for your specific situation.