Thyroid disorders include:

• Hypothyroidism (underactive thyroid). This is the most common type of thyroid disorder, where the thyroid makes too little of the thyroid hormone that your body needs to function properly. It is most often caused by Hashimoto's disease. With this disease, the body's immune system (which normally protects you from disease) thinks the thyroid is a foreign invader and tries to destroy the thyroid. When damage is done to the thyroid, it can become larger (called goiter). Not getting enough iodine in a person's diet can also cause hypothyroidism, but this is more common outside of the United States (in the U.S., many products such as salt and bread are supplemented with iodine, making iodine deficiency rare).
  
  Being female, over 40 years of age, having a close family member with thyroid disease, and recently having had a baby are things that can increase the chance of getting hypothyroidism.

• Hyperthyroidism (overactive thyroid). When the thyroid gland is overactive, it makes too much of the thyroid hormone that your body needs to be healthy. This condition affects women more than men. In young women, hyperthyroidism is most often caused by Graves' disease. With this disease, the body's immune system tricks the thyroid into making too much thyroid hormone. The entire thyroid becomes enlarged and overactive. Older women may get another form of hyperthyroidism (toxic nodular goiter), where overactive thyroid cells group together and form a lump in the neck (called a thyroid nodule) that makes more of the thyroid hormone than the body needs. Some thyroid disorders initially cause overactive thyroid, but at a later point in time cause underactive thyroid, due to damage done to the thyroid gland.

• Postpartum thyroiditis. After giving birth, a woman's thyroid can swell and become larger or inflamed. This can cause changing levels of thyroid hormone in the body. Sometimes high levels can be followed by low levels of thyroid hormone. After 6 months or less, this condition usually goes away with no permanent damage to the thyroid. While common, thyroid disorders after pregnancy are often hard to detect since some of the symptoms, such as having trouble sleeping, fatigue, depression, or weight change are viewed as normal when a woman has a new baby. The symptoms can also be mild. Usually only short-term treatment is required until the thyroid recovers normal function. Sometimes after pregnancy, a woman can get hypothyroidism (underactive thyroid), which persists and needs long-term treatment with medication.

• Thyroid cancer. This type of cancer is most often found as a lump (or nodule) in the thyroid gland. It is not a common type of cancer and most thyroid nodules are benign (not cancer). Other signs of thyroid cancer include swelling in the lymph nodes of the neck and trouble swallowing or breathing. Although anyone can get thyroid cancer, people who as children had head or neck x-ray treatments for tonsillitis or other conditions (from about the 1920s to the 1960s) are more likely to get this cancer. It is treated with surgery, which removes the cancer, sometimes followed by radioactive iodine therapy, which kills the cancer.