How Did I Get an 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.

Can you suddenly get an underactive thyroid?

Autoimmune hypothyroidism can begin suddenly, but in most people it develops slowly over years. The most common form of autoimmune hypothyroidism is called Hashimoto's disease. This can sometimes cause the thyroid to shrink over time.

What is the main cause of thyroid problems?

Problems with the thyroid can be caused by: iodine deficiency. autoimmune diseases, in which the immune system attacks the thyroid, leading either to hyperthyroidism (caused by Graves' disease) or hypothyroidism (caused by Hashimoto's disease) inflammation (which may or may not cause pain), caused by a virus or ...