what causes a underactive thyroid
Most cases of an underactive thyroid are caused by the immune system attacking the thyroid gland and damaging it, or by damage that occurs as a result of treatments for thyroid cancer or an overactive thyroid. condition called Hashimoto's disease is the most common type of autoimmune reaction that causes an underactive thyroid. It's not clear what causes Hashimotoâs disease, but it runs in families. It's also common in people with another immune system disorder, such as type 1 diabetes and vitiligo.