Causes of thyroid cancer

We don’t yet know what causes thyroid cancer in most people, but some things may increase the risk of developing it.

What causes thyroid cancer?

We don’t yet know what causes thyroid cancer in most people. But there are a number of things that may increase your risk of developing it. These are called risk factors. Having a particular risk factor doesn’t mean you will definitely get thyroid cancer. And sometimes people without any known risk factors will develop cancer.

The information here is about papillary and follicular thyroid cancers. Medullary thyroid cancer and anaplastic thyroid cancer have different risk factors.

If you are worried about thyroid cancer and would like to talk to someone, we're here. You can:

Benign thyroid disease

Having an overactive or underactive thyroid (hyperthyroidism and hypothyroidism) does not increase your risk of developing thyroid cancer.

If you have certain types of non-cancerous (benign) thyroid disease, you are slightly more likely to develop thyroid cancer. These types of benign thyroid disease include:

  • an enlarged thyroid (goitre)
  • thyroid nodules (adenomas)
  • inflammation of the thyroid (thyroiditis).

Benign thyroid disease can run in families. You are more at risk of getting thyroid cancer if you have family members with benign thyroid disease. The risk is higher if more than one member of your family is affected.

Exposure to radiation

If you have had radiotherapy treatment to the neck area, particularly as a child or young adult, you have a higher risk of developing thyroid cancer many years later.

Exposure to high levels of radiation in the environment can also increase your risk. For example, accidental exposure can happen after a nuclear accident like Chernobyl. But only a small number of thyroid cancers are caused by radiation exposure.

Family history

Your risk of developing thyroid cancer is higher if you have a close relative (parent, brother, sister or child) with thyroid cancer. Your risk is still quite small, because thyroid cancer is rare.

There is also a slightly increased risk of developing thyroid cancer if you have inherited an altered gene that causes a bowel condition called familial adenomatous polyposis (FAP). Family members of a person with FAP can have tests to see if they have the same altered gene.


It is thought that people who are overweight may have a higher risk of getting thyroid cancer. A healthy diet and regular exercise may reduce the risk.

Thyroid cancer risk in women

Thyroid cancer is more common in women than men. There may be a link to female hormones.