How Common Are Benign Thyroid Nodules?

Benign thyroid nodules are remarkably widespread. If you have one, you’re far from alone. Healthcare providers detect thyroid nodules in approximately 5% to 7% of adults during routine physical examinations. However, when ultrasound imaging is used, the picture becomes even clearer—studies reveal that between 20% and 76% of adults actually have thyroid nodules, even if they don’t know it.^[1] These growths are also found incidentally when imaging is performed for completely unrelated reasons, appearing on about 16% of neck scans done for other purposes.^[14]

The good news is that the vast majority of detected nodules in adults are noncancerous, or benign—a term doctors use to describe growths that aren’t cancer. More than 90% of thyroid nodules discovered in adults fall into this category.^[1] Thyroid nodules are about four times more common in women than in men, and their occurrence increases with age.^[1] By the time people reach 70 years of age, around 80% will have at least one nodule, with approximately 90% to 95% of all nodules being benign.^[5]

In autopsy studies—examinations done after death to understand disease patterns—thyroid nodules were found in 3% to 4.3% of cases, though the actual prevalence in living people appears much higher when modern imaging is used.^[3] Thyroid nodules are less common in children, but when they do occur in younger individuals, they require careful evaluation.^[1]

What Causes Benign Thyroid Nodules?

The exact reason why most thyroid nodules form remains unclear to researchers. In many cases, these growths develop without any obvious cause. However, certain environmental and genetic factors have been identified that may contribute to their development.^[3]

One well-known environmental factor is iodine deficiency—a lack of iodine in the diet. Iodine is a mineral necessary for your thyroid gland to produce hormones that regulate metabolism, body temperature, heart rate, and digestion. When the body doesn’t get enough iodine, the thyroid may develop nodules. This is the most common cause of thyroid nodules worldwide, especially in underdeveloped countries where iodine isn’t added to food.^[3] The introduction of iodized salt in 1924 virtually eliminated iodine deficiency disorders in the United States, making this less of a concern in developed nations.^[14]

Most thyroid nodules—referred to medically as thyroid adenomas when they are benign tumors—are sporadic and not hereditary. This means they aren’t typically passed down through families.^[3] However, in rare cases, genetic mutations in genes such as BRAF, RET, and KRAS, as well as genetic rearrangement of the PAX8-PPAR gene, are strongly associated with the development of thyroid adenomas.^[3] Advances in molecular techniques have helped researchers better understand the genetic basis of these nodules and distinguish benign from malignant tumors.^[3]

Thyroid nodules can be classified into different types based on their structure. Some are solitary, meaning there’s just one nodule, while others are multiple, with several nodules present. They can also be described as cystic, which means they’re filled with fluid, or solid, meaning they’re made up of thyroid tissue.^[1]

Who Is at Risk for Developing Thyroid Nodules?

Anyone can develop a thyroid nodule, including children and adults. However, certain groups of people are more likely to develop them. As mentioned, women are significantly more affected than men, with nodules occurring about four times more often in females.^[1] Age also plays a role—nodules become more common as people get older.^[1]

Several other factors can increase your risk of developing thyroid nodules. A history of radiation exposure to the head, neck, or chest—such as from cancer treatments or occupational exposure—is a known risk factor.^[1] People with a family history of thyroid nodules or thyroid cancer are also at higher risk.^[1]

Other conditions and lifestyle factors associated with increased thyroid nodule risk include iron-deficiency anemia (a condition where your blood doesn’t have enough healthy red blood cells), smoking, obesity, metabolic syndrome (a cluster of conditions including high blood pressure, high blood sugar, and abnormal cholesterol levels), alcohol consumption, increased levels of insulin-like growth factor-1 (a hormone that promotes growth), and even the presence of uterine fibroids.^[1]

People living in countries where food isn’t fortified with iodine are at greater risk because their bodies may not get enough of this essential mineral to maintain normal thyroid function.^[1] In the United States and other developed nations, iodine fortification of salt has greatly reduced this risk.^[14]

What Symptoms Do Benign Thyroid Nodules Cause?

Most people with benign thyroid nodules don’t experience any symptoms at all. These nodules are often discovered incidentally—by accident—during a routine physical examination or when imaging tests such as CT scans or ultrasound are performed for completely unrelated reasons.^[1][2] Occasionally, patients themselves discover a thyroid nodule by noticing a lump in their neck while looking in a mirror, buttoning their collar, or fastening a necklace.^[7]

However, if you have several nodules or if they become large, you may be able to see or feel them as a swelling at the base of your neck.^[2] In rare cases, nodules can grow large enough to cause noticeable symptoms. These may include trouble with swallowing or breathing, which occurs when the nodule presses on the tube that connects your throat to your stomach (the esophagus) or on your windpipe.^[1][2]

Some people may experience hoarseness or voice changes if the nodule presses on the nerves that control the vocal cords, though this symptom is usually related to thyroid cancer rather than benign nodules.^[6] Pain in the front of the neck is another possible symptom, though it’s uncommon.^[1] Large nodules may also cause an enlargement of the entire thyroid gland, a condition known as goiter.^[1]

Some benign thyroid nodules are “hyperfunctioning,” meaning they produce excess amounts of thyroid hormone. This can lead to a condition called hyperthyroidism, where your body has too much thyroid hormone. Symptoms of hyperthyroidism include rapid heartbeat or heart palpitations, feeling shaky or nervous, unexplained weight loss despite increased appetite, diarrhea and more frequent bowel movements, difficulty sleeping, increased sweating, and light or missed menstrual periods in women.^[1][2]

On the other hand, thyroid nodules may sometimes be associated with low thyroid hormone levels, a condition called hypothyroidism. Symptoms of hypothyroidism include fatigue, numbness and tingling in your hands, weight gain, dry and coarse skin and hair, constipation, depression, and frequent or heavy menstrual periods.^[1]

Can Benign Thyroid Nodules Be Prevented?

Since researchers don’t fully understand why most thyroid nodules form, there aren’t specific prevention strategies that can guarantee you won’t develop one. However, maintaining adequate iodine intake is one clear way to reduce risk, particularly in areas where iodine deficiency is common. In countries like the United States, where iodized salt is widely available, this is less of a concern.^[14]

Avoiding unnecessary radiation exposure to the head, neck, or chest may also help reduce risk, as radiation is a known factor that can contribute to nodule formation.^[1] Managing other risk factors, such as maintaining a healthy weight, not smoking, and limiting alcohol consumption, may also play a role, though these factors are just associations and not proven causes.^[1]

Regular medical checkups allow for early detection of thyroid nodules, even if they’re not causing symptoms. The U.S. Preventive Services Task Force recommends against routine screening for thyroid cancer with neck palpation or ultrasound in people without symptoms, as screening can lead to overdiagnosis and overtreatment without improving outcomes.^[14] However, if you have risk factors or symptoms, your doctor may recommend evaluation.

How Do Benign Thyroid Nodules Affect the Body?

Understanding how benign thyroid nodules affect the body requires looking at how the thyroid gland normally functions. The thyroid is a small, butterfly-shaped endocrine gland—a gland that produces hormones—located in your neck, just below your Adam’s apple. It weighs about 20 to 30 grams in adults.^[3] The thyroid’s job is to make two main hormones: thyroxine (also called T4) and triiodothyronine (also called T3). These hormones are released into the bloodstream and carried to every tissue in the body, where they help regulate metabolism, body temperature, mood, heart rate, pulse, and digestion.^[1][7]

When a benign nodule forms, it represents an abnormal growth of thyroid cells within the gland. In most cases, these nodules are inactive and don’t interfere with normal thyroid function. Thyroid tests, such as measurements of thyroid-stimulating hormone (TSH), which is produced by the pituitary gland in your brain and tells the thyroid to make hormones, are typically normal even when a nodule is present.^[7] This means the nodule is just sitting there, not causing any functional problems.

However, some benign nodules are “active,” meaning they produce thyroid hormone on their own. These are called toxic thyroid adenomas or autonomously functioning thyroid nodules (AFTN). When a nodule produces excess thyroid hormone, it can cause biochemical and clinical hyperthyroidism, leading to the symptoms described earlier, such as rapid heartbeat, weight loss, and nervousness.^[3] Patients with hyperfunctioning nodules may require treatment to manage these symptoms.^[6]

Large benign nodules can physically affect nearby structures in the neck. As they grow, they can press on the windpipe or esophagus, causing symptoms like difficulty breathing, swallowing, or a sensation of something stuck in the throat.^[7][9] These nodules may also cause an enlargement of the thyroid gland visible from the outside, known as goiter.^[1] A goiter can be cosmetically concerning and, when large, can cause discomfort or pressure, particularly when lying down.^[9]

In rare cases, nodules may be associated with inflammation of the thyroid, a condition called thyroiditis, which can cause pain, hyperthyroidism followed by hypothyroidism, or other thyroid function abnormalities.^[4] However, most benign nodules don’t cause inflammation or long-term damage to thyroid function.

It’s important to note that while most thyroid nodules are benign and don’t cause health problems, they can sometimes be a sign of or cause of thyroid disease. Additionally, even though the vast majority are not cancer, some thyroid nodules do contain thyroid cancer, which is why proper evaluation is essential.^[1]