Hashimoto’s disease, also called chronic lymphocytic thyroiditis or autoimmune thyroiditis, is an autoimmune disease. An autoimmune disease is a disorder in which the body’s immune system attacks the body’s own cells and organs. Normally, the immune system protects the body from infection by identifying and destroying bacteria, viruses, and other potentially harmful foreign substances.
In Hashimoto’s disease, the immune system attacks the thyroid gland, causing inflammation and interfering with its ability to produce thyroid hormones. Large numbers of white blood cells called lymphocytes accumulate in the thyroid. Lymphocytes make the antibodies that start the autoimmune process.
Hashimoto’s disease often leads to reduced thyroid function or hypothyroidism.
Hypothyroidism is a disorder that occurs when the thyroid doesn’t make enough thyroid hormone for the body’s needs. Thyroid hormones regulate metabolism—the way the body uses energy—and affect nearly every organ in the body. Without enough thyroid hormone, many of the body’s functions slow down. Hashimoto’s disease is the most common cause of hypothyroidism in the United States.