An underactive thyroid, also known as hypothyroidism, can cause a variety of symptoms such as fatigue, dry skin, changes in the menstrual cycle and constipation, according to WebMD. Other symptoms may include depression, slow heart rate, unexplained weight gain, dry hair or hair loss.
Many of the symptoms associated with an underactive thyroid may mimic other conditions or be vague in nature, states WebMD. Some groups of people are at a higher risk for developing hypothyroidism such as people with autoimmune disorders, bipolar disorder or Down syndrome. Growing older, being white or Asian, and people with prematurely graying hair are also at a higher risk.