Hypothyroidism is a condition where the thyroid gland does not produce enough thyroid hormones. The thyroid is in the neck, located in front of the windpipe (trachea). The thyroid gland produces two thyroid hormones, triiodothyronine (T3) and thyroxine (T4), which regulate metabolism, brain development, breathing, heart and nervous system functions, and body temperature among many other functions. An underactive thyroid leads to fatigue, depression, constipation, feeling cold, elevated blood cholesterol, fertility difficulties or menstrual changes, muscle stiffness/aches/tenderness, puffy, sensitive face, dry skin, and weight gain. Hypothyroidism is mostly caused by Hashimoto’s thyroiditis, an autoimmune condition where the immune system attacks the thyroid gland and causes chronic thyroid inflammation. The inflammation can reduce thyroid function. Hypothyroidism is usually hereditary, and there are no known methods to prevent it. Other causes include surgical removal of a portion or all of the thyroid, radiation therapy from cancer treatment, and medications used to treat psychological, cancer and heart conditions. Hypothyroidism can happen at any age and in any gender, although it is more common in women. Diagnosing hypothyroidism involves a physical examination and review of medical history by a doctor, and a thyroid function test. The thyroid function test measures the level of thyroid-stimulating hormone (TSH) that the pituitary gland is making. A high level of TSH indicates an underactive thyroid, while a low level of TSH suggests the body is trying to stop excessive thyroid hormone production. A thyroxine (T4) level test is also useful in diagnosing hypothyroidism. A low level of T4 and a high level of TSH suggests hypothyroidism. Treatment for an underactive thyroid involves taking daily hormone replacement tablets of levothyroxine to raise thyroxine levels. It is a life-long treatment. Other recommendations are lifestyle improvements - eat a balanced diet, monitor soy intake, avoid excessive fiber consumption, and consult a therapist for emotional support. In adults, untreated hypothyroidism can lead to heart disease, goiter, pregnancy problems and a life-threatening condition called myxoedema coma; in infants it can cause jaundice, a large, protruding tongue, difficulty breathing, hoarse crying, umbilical hernia and excessive sleepiness.