This is a condition in which the person does not make enough thyroid hormone. It is most common in adult women and causes symptoms such as cold, pale, dry skin, brittle hair and nails, fatigue, weight gain and sluggishness. When the thyroid is not making enough hormone at birth, it is called congenital hypothyroidism. Hypothyroidism is treated by a medication that replaces the natural thyroid hormone the person cannot make on his or her own.