The thyroid, a butterfly-shaped gland in the neck, is primarily responsible for coordinating energy, growth and metabolism in your body. Problems can occur when this hormone’s levels are too high or low. At least 30 million Americans have a thyroid disorder and half (15 million) are undiagnosed. What causes your thyroid to malfunction? Researchers aren’t entirely sure, but believe that genetics, an autoimmune attack, stress, toxins in the environment can play a part in thyroid disorders. Here are signs that your thyroid may not be working properly.

1. Weight gain

Unexpected weight gain is common symptom of hypothyroidism, which is a low thyroid hormone level. When thyroid levels are low, your body’s metabolism switches modes. Instead of burning calories for growth and activity, the amount of energy you use at rest, decreases. As a result, your body tends to store more calories from your diet as fat.

2. You’re exhausted

The thyroid hormone controls energy balance and can influence whether you feel alert or sleepy. Low-thyroid sufferers often feel unrested, even though they may be sleeping more. Feeling perpetually sleepy without a good explanation could be a sign of an underactive thyroid.

3. You’re depressed

Depression can also be a sign of an underactive thyroid, though researchers aren’t entirely sure why. However, it could be a mental symptom of an overall decrease in energy and health.

4. Hair loss

Your hair follicles are regulated by thyroid hormone. Low thyroid hormone causes hair follicles to stop regenerating, resulting in hair loss. This will typically improve when the thyroid issue is treated.

5. Loss of interest in sex

Having little or no desire for sex can be a side effect of a thyroid disorder. Too little thyroid hormone often contributes to a lower sex drive.