Underactive Thyroid

What Causes an Underactive Thyroid?

An underactive thyroid is most often caused by conditions that affect the thyroid gland. The most common condition is Hashimoto's thyroiditis. This is a type of autoimmune thyroid disease in which the immune system attacks and destroys the thyroid gland. This condition is more common in older women. It is also the most common cause of hypothyroidism in children.
Other causes of an underactive thyroid include:
  • Surgical removal of part or all of the thyroid gland
  • Radiation treatment of the thyroid
  • Thyroiditis (inflammation of the thyroid gland)
  • Congenital hypothyroidism (hypothyroidism that is present at birth)
  • Certain medications
  • Iodine deficiency or excess.
(Click Causes of Underactive Thyroid to learn more about these conditions, including other possible causes outside of the thyroid gland.)
Certain factors can increase a person's chances of developing an underactive thyroid, including age, gender, and a family history of thyroid disease (see Hypothyroidism Risk Factors for more information).

Signs and Symptoms of an Underactive Thyroid

Thyroid hormones play a role in the normal functioning of many different parts of the body, including:
  • The skin
  • Blood
  • Heart and blood vessels
  • The nervous system
  • The reproductive system
  • The digestive system.
Therefore, when a person has an underactive thyroid, many different areas of the body can be affected.
Symptoms do vary from person to person. Some people may have no symptoms, vague complaints (such as feeling tired or sluggish), or symptoms often seen in older people (dry skin, constipation, and sensitivity to the cold).
After a couple of years, other, more obvious symptoms and signs of hypothyroidism may start to appear, such as:
  • Weight gain
  • Puffy face
  • Joint and muscle pain, aches, and stiffness
  • Dry, thinning, or coarse hair
  • Brittle nails
  • Decreased sweating
  • Heavy or irregular menstrual periods
  • Depression
  • Difficulty catching your breath (extreme shortness of breath) when exercising.
(Click Underactive Thyroid Symptoms for a complete list of possible symptoms.)
Last reviewed by: Arthur Schoenstadt, MD
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