Hypothyroidism is a condition that is characterized by an underactive thyroid. It is a condition that is caused by the thyroid gland not producing enough thyroid hormone. Hypothyroidism is also known as underactive thyroid disease. It is quite common. The thyroid gland is located in the front of the lower portion of the neck. Hormones are released from the thyroid gland into the bloodstream. These thyroid hormones affect almost every part of the body. When there is an imbalance in the thyroid hormones, problem can arise.