Thyroiditis is inflammation of the thyroid gland in the neck. This inflammation may result in hypothyroidism, when the thyroid produces too few hormones, or hyperthyroidism, when the thyroid produces too many hormones. There are many types of thyroiditis.
Thyroiditis is usually related to a problem with the body's immune system. Antibodies meant to attack foreign substances instead attack the body's own thyroid. When this happens, the thyroid doesn't work as it should. This type of thyroiditis is called autoimmune thyroiditis or Hashimoto's thyroiditis.
Sometimes thyroiditis happens after a woman gives birth to a baby. Thyroiditis may also be caused by some medicines. Or it can be caused by an infection with a virus or bacteria.