What will happen if thyroid disease is not treated?

Thyroid: It depends on the age and how severe the hypothyroidism is. In children under 3 yrs old developmental problems or even retardation could occur. Growth failure could be a symptom in older kids. Others include forgetfulness, depression, mood swings, dry skin, coarse hair, constipation, lethargy, cold intolerance, exercise intolerance, irregular or heavy periods, and weight gain.