What is the most common form of hypothyroidism?

The most common form of hypothyroidism is Hashimoto's thyroiditis, which is an autoimmune disorder where the body's immune system attacks the thyroid gland. This condition leads to chronic inflammation of the thyroid and results in the underproduction of thyroid hormones. It is prevalent particularly because it can develop slowly over years without obvious symptoms, meaning many individuals may not be aware they have the condition until routine blood tests indicate low thyroid hormone levels.

Hashimoto's thyroiditis is significant in the landscape of hypothyroidism, as it accounts for a large percentage of cases in developed countries. Factors such as genetics, environmental triggers, and certain hormonal changes can contribute to its onset, highlighting its complexity and the range of influences that can lead to thyroid dysfunction.

In contrast, other forms of hypothyroidism mentioned—like cretinism, which is seen in infancy as a result of severe hypothyroidism; subclinical hypothyroidism, which is a milder form without overt symptoms and often managed differently; and secondary hypothyroidism, due to a failure of the pituitary gland, are less common in comparison to Hashimoto's thyroiditis.