Autoimmune thyroiditis is an autoimmune disease that affects the thyroid gland. Autoimmune thyroiditis is ten times more common in women than in men. Symptoms usually first appear between the ages of 30 and 50. The overall incidence increases with age in both men and women. Autoimmune thyroiditis is characterized by antibodies to thyroid antigens. The thyroid gland is damaged and gradually grows. Over time, autoimmune thyroiditis leads to hypothyroidism, in which the body lacks thyroid hormones. Hypothyroidism is accompanied by weight gain, dry skin, and increased fatigue.