Causes of thyroid cancer

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

What causes thyroid cancer?

We do not know what causes thyroid cancer in most people. But there are some things that may increase your risk of developing it. These are called risk factors. Having one or more risk factors does not mean you will get thyroid cancer. And if you do not have any risk factors, it does not mean you will not get 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.

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

  • an enlarged thyroid (goitre)
  • thyroid nodules (adenomas)
  • inflammation of the thyroid (thyroiditis) ¬– including Hashimoto’s 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 family member is affected.

Exposure to radiation

If you have had radiotherapy treatment to the neck area, you have a higher risk of developing thyroid cancer many years later. This risk is higher if you were a child or young adult at the time.

Being exposed to high levels of radiation in the environment can also increase your risk. For example, accidental exposure after a nuclear accident like Chernobyl. This is very rare.

It is important to remember that only a small number of thyroid cancers are caused by any kind of radiation exposure.

Family history

Your risk of developing thyroid cancer is higher if you have a close family member (relative) with thyroid cancer. A close relative is:

  • a parent
  • a brother or sister (sibling)
  • your child.

The risk is still small because thyroid cancer is rare.

Having an inherited altered gene called familial adenomatous polyposis (FAP) can also slightly increase your risk of thyroid cancer. Family members of a person with FAP can have tests to see if they have the same altered gene.

People with PTEN Hamartoma tumour syndrome have a higher risk of thyroid cancer. This is a group of rare conditions which includes Cowden’s syndrome.


Being overweight may increase the risk of getting thyroid cancer. A healthy diet and regular exercise may reduce the risk.


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

About our information

  • References

    Below is a sample of the sources used in our thyroid cancer information. If you would like more information about the sources we use, please contact us at

    British Medical Journal. Best Practice Guidelines, Thyroid cancer. 2020.

    European Society Medical Oncology (ESMO): Thyroid cancer, Clinical Practice Guidelines for Diagnosis, Treatment and Follow-up. 2019.

    National Institute for Health and Care Excellence (NICE). TA535: Lenvatinib and Sorafenib for treating differentiated thyroid cancer after radioactive iodine. 2018. [accessed May 2021].

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Professor Nick Reed, Consultant Clinical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
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We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 June 2021
Next review: 01 June 2024

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.