Alopecia
A severe and prolonged overactive thyroid can cause loss of hair. The loss is diffuse and involves the whole scalp rather than discrete areas. Some forms of this condition appear suddenly and are diagnosed early, while others may have been present for months or years before diagnosis.
Hair loss due to this disease becomes apparent several months after the onset of this condition. [5] In such cases, the hair loss may follow the treatment for the thyroid, and can be a side effect of the medication, leading to the withdrawal of treatment, which may worsen the hair loss. The hair appears uniformly sparse. Regrowth is usual with successful treatment of the thyroid disorder, though it will take several months and may be incomplete. It is unusual for the mild stage of this condition or short-lived thyroid problems to cause hair loss.