Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. (a deficiency of thyroid hormone). Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or hypothalamus. It can result from a lack of a thyroid gland or from iodine-131 treatment, and can also be associated with increased stress. Severe hypothyroidism in infants can result in cretinism.