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12 Surprising Symptoms of an Underactive Thyroid

Learn about unexpected thyroid symptoms and how they can affect your health.
12 Surprising Symptoms of an Underactive Thyroid
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Your thyroid produces thyroid hormones – T4 and T3 – that help regulate your body’s metabolism. Every cell in your body needs sufficient levels of thyroid hormone to function correctly. A lack of thyroid hormones, the characteristic marker of hypothyroidism, causes your bodily processes to slow down and change. This results in the symptoms of hypothyroidism.

Often, fatigue and weight gain steal the spotlight when it comes to hypothyroidism symptoms. But there are many other symptoms, and some may even surprise you.

Understanding these lesser-known symptoms is essential to recognizing and managing hypothyroidism effectively. Let’s take a look at 12 surprising and lesser-known symptoms of hypothyroidism.

1. Headaches

The Journal of Headache and Pain found a high prevalence of hypothyroidism in those who experience migraine headaches. Around 30% of people with an underactive thyroid experience headaches. A recent study echoed these results, showing that the incidence of migraine is higher among those with a thyroid disorder, especially in mild (subclinical) hypothyroidism.

It remains unclear whether hypothyroidism is the cause of headaches, though it’s a reasonable assumption since the brain relies on thyroid hormone for optimal functioning and overall health. Thyroid hormones also help in the development and functioning of brain cells and the production of neurotransmitters, which are essential for communication between nerve cells. 

Additionally, fatigue, a common symptom of hypothyroidism, is often associated with migraines and may play a role in triggering migraine headaches.

2. Memory changes

When thyroid levels are low, one’s ability to think clearly and remember things changes. Some people refer to this symptom as “brain fog.”

Low thyroid levels can also affect your other cognitive functions, such as:

  • Attention and concentration
  • Perceptual function (how the brain translates sensory information and acts upon it)
  • Language (how one speaks or understands what others are saying)
  • Psychomotor functions (how well your brain controls your movement and coordination)
  • Executive tasks like organizing, prioritizing, or working memory

The degree of memory changes varies from person to person. Those with a mild drop in their thyroid hormone levels may not notice a significant change in their memory. However, those with deficient thyroid hormone levels may have a more noticeable change.

3. Mood swings

An underactive thyroid can throw your hormonal balance off, resulting in mood changes, such as feelings of sadness, anxiety, and irritability.

Hormonal imbalance doesn’t just refer to thyroid hormones. Other hormones –  like serotonin and somatostatin – work in your central nervous system, affecting mood regulation and your thyroid levels. For example, somatostatin levels were lower in those with depression based on a 2022 review. As a result, TSH levels were higher. A high TSH level reduces thyroid hormone production, causing hypothyroidism.

Overt hypothyroidism and depression have similar symptoms, including slowed thought and speech, decreased attentiveness, or lack of motivation. These similarities sometimes lead to a missed diagnosis or incorrect diagnosis of clinical depression.

4. Digestive issues

As mentioned, low thyroid hormone causes your body functions to slow down, and your digestive tract is no exception. Feelings of bloating or constant constipation are common digestive symptoms that an underactive thyroid can contribute to.

Too little thyroid hormone slows gastric motility, which is the processing of moving food through the digestive tract. This delay in food transit can cause the food to sit in your GI tract for an extended time. In more severe cases of slowed gastric motility, an overgrowth of bacteria can occur. This can result in small intestinal bacterial overgrowth (SIBO), causing additional GI discomfort, nutrient deficiencies, and diarrhea.

5. Heartburn

Undiagnosed or undertreated hypothyroidism can prevent the lower esophageal sphincter (LES) from doing its job - stopping stomach contents from going back into your esophagus. When the LES doesn’t function properly, stomach contents, including acid, can escape and travel up your esophagus. This causes symptoms of heartburn, a burning (sometimes painful) sensation in your chest. You may also notice a bitter or acidic taste in your mouth or even have trouble swallowing.

You may find heartburn comes and goes. And severity can differ depending on the foods you eat. For example, spicy foods are common heartburn triggers. But, constant heartburn may also be a sign of gastroesophageal reflux disease (GERD), which requires a visit to your provider.

6. Dry skin

Dry skin is a common symptom experienced by individuals with hypothyroidism. It is characterized by rough, scaly, and flaky skin that may feel tight and itchy. This condition typically affects the face, hands, arms, and legs. Dry skin caused by hypothyroidism is often resistant to moisturizers and may persist even with proper skincare routines.

Skin cell turn occurs when new process where new cells replace old. This constant process takes 40 to 56 days. Since body processes slow down in those with undiagnosed hypothyroidism, the time it takes for the skin cells to turnover increases. Because of this, old cells stay on your skin longer, resulting in dry, rough, and scaly skin.

Another reason hypothyroidism leads to dry skin is the reduced sebum production. Sebum is an oily substance the sebaceous glands produce to lubricate and protect the skin. Inadequate hormone levels hinder the normal production of sebum, resulting in dryness and a compromised skin barrier.

Hypothyroidism can also affect the skin’s ability to retain moisture. The natural moisture barrier, which helps seal in hydration, becomes weakened, leading to increased water loss from the skin. This further worsens the dryness, making it difficult for the skin to stay hydrated.

7. Sensitivity to cold

The inability to tolerate cold temperatures is another classic sign of hypothyroidism.

The hypothalamus in the brain acts as a thermostat by directing the thyroid gland to increase or decrease your body’s metabolism. As cells work, they generate heat, which regulates body temperature.

A lack of thyroid hormone slows down your metabolism. And a slower metabolism means your cells are making less heat. The result is an inability to tolerate cold temperatures. You may notice that your hands and feet are frequently cold, you shiver even when bundled up, or you’re still feeling chilled when others feel warm.

8. Menstrual irregularities

Insufficient thyroid hormone levels may cause several menstrual irregularities, from heavy, prolonged periods to infrequent or absent periods. Roughly 80% of women with hypothyroidism have some sort of menstrual irregularity during their childbearing years.

While heavy menstrual bleeding is common, absent or infrequent menstruation is commonly reported in those with an underactive thyroid. This may occur due to a possible increase in thyrotropin-releasing hormone (TRH).

The hypothalamus releases TRH. TRH triggers the release of thyroid-stimulating hormone (TSH) and prolactin from the pituitary gland. Too much prolactin, often referred to as the “milk hormone,” can interfere with estrogen production, resulting in

  • Infrequent or absent periods
  • Unwanted milk production
  • Symptoms of menopause

Of course, while undiagnosed or undertreated hypothyroidism is one potential cause of menstrual irregularities, there are other possible diagnoses. You should consult with your care team if you have menstrual irregularities.

9. Fertility issues

A lack of thyroid hormone can change the levels of your reproductive hormones, especially estrogen and androgens. These shifts in estrogen and androgen levels can alter TSH levels. As a result, it may be more difficult for some people to get pregnant.

Furthermore, these hormonal shifts can result in irregular ovulation. Irregular ovulation may make it harder to get pregnant. Based on a 2023 review, higher TSH levels during the childbearing years are linked to poor ovarian (egg) reserves.

Low thyroid hormone levels can also alter sperm number, motility, and shape. These changes can make it harder for sperm to reach the egg, increasing the risk of thyroid-related infertility

10. Muscle aches and weakness

Muscle aches and weakness can be common symptoms associated with hypothyroidism. Muscles depend on thyroid hormone for proper muscle contractions. During a muscle contraction, muscles tighten, shorten, or lengthen to help you complete an activity such as walking or typing. Low thyroid hormone levels limit the strength and how often your muscles contract. The result is weak, stiff, and achy muscles.

Additionally, low thyroid hormone levels can also affect the muscle tissues directly. Lack of proper hormone levels can disrupt the balance of electrolytes, such as calcium and magnesium, essential for maintaining muscle health. This imbalance can lead to muscle pain, cramps, spasms, and overall weakness.

Hypothyroidism can also contribute to the accumulation of fluid in the tissues, a condition known as edema. This fluid retention can affect the muscles, leading to swelling, stiffness, and overall discomfort.

11. Thinning hair

Did you know you shed up to 150 hairs per day? However, new growth usually replaces them immediately, so you generally don’t notice.

A sluggish thyroid prolongs the life cycle of your hair. So, when you shed your old hair, new hair isn’t already there to replace it, causing hair loss. Because of this, you may feel your hair appears thinner or even notice that you’ve developed small bald spots. You may even notice hair loss on your eyebrows. Generally, eyebrow hair loss starts on the outer ends.

The hair on your head is not the only hair affected by low thyroid hormone levels. You may notice hair loss on your eyebrows. Eyebrow hair loss on the outer edges is typically a characteristic sign of hypothyroidism.

Because the hair growing and shedding cycle can slow down, it may be three to four months after the onset of hypothyroidism before you start noticing thyroid-related hair loss.

Note: You may also experience changes in your hair texture, such as dry, brittle hair and increased coarseness. 

12. Throat tightness

Inflammation or swelling of the thyroid gland, also known as goiter, can cause a feeling of tightness in your throat. It may feel like wearing a turtleneck or a tight collar on your shirt.

Goiter is usually painless, but as it grows, it can cause symptoms such as:

  • Difficulty swallowing
  • Trouble breathing or catching your breath
  • Sore throat
  • Voice changes

You can perform a simple at-home neck check to help with early detection. A self-exam can help you find lumps or enlargements that may indicate a thyroid condition.

A note from Paloma Health

The good news is that most of these symptoms improve with proper hypothyroidism management!

The first step, though, is evaluating how well your thyroid functions. You can do this using Paloma Health’s at-home testing kit. Our blood test kit measures the most common thyroid biomarkers - TSH, T4, T3 - needed to determine a thyroid disorder. Your results will determine if there is a likelihood of thyroid issues and whether you need further evaluation by a thyroid specialist.

So, if you have persistent symptoms as described above, talk with your healthcare provider. There may be an underlying health condition besides hypothyroidism causing your symptoms. And if they recommend testing your thyroid function, order your home testing kit today!


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Emilie White, PharmD

Clinical Pharmacist and Medical Blogger

Emilie White, PharmD is a clinical pharmacist with over a decade of providing direct patient care to those hospitalized. She received her Doctor of Pharmacy degree from Massachusetts College of Pharmacy and Health Sciences. After graduation, Emilie completed a postgraduate pharmacy residency at Bon Secours Memorial Regional Medical Center in Virginia. Her background includes caring for critical care, internal medicine, and surgical patients.

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