What Happens If an Underactive Thyroid Goes Untreated 

Symptoms of an underactive thyroid often are mistaken for other conditions, so people may ignore the condition. But many problems can arise if the thyroid goes untreated. Some problems are not as serious as others, while some can be deadly. 

Patients may notice the following symptoms, which a doctor should examine:

• weight gain;
• dry skin and hair;
• hair loss;
• fatigue; and
• muscle aches. 

The Mayo Clinic lists these and other complications that may indicate an underactive thyroid: 

• high LDL cholesterol (the "bad" cholesterol);
• a goiter, or lump in the throat, which can be unsightly and affect swallowing and breathing;
• peripheral nerve damage;
• depression and other mental health problems;
• infertility stemming from problems with ovulation;
• birth defects if the mother has hypothyroidism; and
• more.