As soon as our body starts to feel off, we immediately consider two explanations: Mercury is in retrograde, or there must be something wrong with our thyroid, according to Google. (Hint: Only one has solid science to back it up.) But can we really blame unwanted symptoms—from exhaustion to weight gain—on the thyroid, or is our scapegoating unwarranted?

The Need-to-Know

Turns out, you're not wrong for thinking of it first. Almost every system in our body depends in some part on hormones produced by the thyroid, says Jordan Geller, M.D., attending physician and past clinical chief in the Division of Endocrinology at Cedars-Sinai in Los Angeles.

The gland, found in the front part of the neck and about the size and shape of a small butterfly, plays a role in metabolism, growth, and just about everything in your body, from the brains to the bowels to the heart, skin, and digestive system.

How does it work? The thyroid produces a hormone, thyroxine (or T4) that goes out to all our organs. Once it arrives at its destination organ, it's converted into another hormone, triiodothyronine (or T3). There, it sets the pace for your cells, helping them do what they're supposed to do. Basically, those hormones tell your heart to keep beating, your liver to keep metabolizing, and so on.

You Might Like {{displayTitle}} READ

Our body's dependency on thryoid hormones means that as soon as there's a problem with it, we feel it in many ways, says Douglas S. Ross, M.D., co-director of Thyroid Associates at Massachusetts General Hospital. Hyperthyroidism, when your thyroid produces too many hormones, may make all of the bodily systems speed up, leading to consequences like feeling nervous, anxious, sweaty, or losing a lot of weight.

On the flip side, hypothyroidism, when the thyroid produces too few hormones, makes your body seem to work in slow motion. Symptoms include feeling depressed, tired, and bloated; dry and brittle skin and hair; and weight gain, despite a healthy diet.

So why, exactly, does this happen? In both hyper- and hypothyroidism, an autoimmune condition is usually to blame. Hyperthyroidism is associated with Graves' disease, while hypothyroidism is linked to Hashimoto's disease. In both cases, something sets the body off and causes the immune system to malfunction, targeting the thyroid and making it skew production one way or the other.

Doctors aren't sure what causes this, but hyperthyroidism is more common in younger women, while hypothyroidism can show up at any age, says Terry Davies, M.D., professor of endocrinology, diabetes and bone disease, at Mount Sinai's Icahn School of Medicine.

Plus, thyroid disease tends to run in families and is fairly common—more than 12 percent of the U.S. population will develop a thyroid condition in their lifetime, according to the American Thyroid Assocation, with 60 percent of those people unaware of their condition.

Your Action Plan

The tricky thing about thryoid diseases are that all of the symptoms are non-specific—meaning you could have one symptom, or all of them, and it still doesn't necessarily mean your thyroid is the cause, Davies says.

A blood test is the only way to nail down if your thyroid is to blame for your symptoms.

Because of that, a blood test is the only way to nail down if your thyroid is to blame. Luckily, the test, known as a thyroid stimulating hormone (TSH) test, is quick, easy, and doesn't lie (despite some online claims, thyroid tests are very accurate, Davies says). Talk to your general practitioner, and he or she can prescribe it, usually with same-day results.

Between the wide variety of symptoms and readily available cures, all of the doctors agreed that there's no reason why you shouldn't get checked if you have a sneaking suspicion something's off. Other causes may include anemia (it shares hypothyroidism symptoms like fatigue, weakness, and chills), or even simply not sleeping enough, but there's no way to know without a test.

The Takeaway

Thyroid problems are fairly common, so if you think something's up, you could be right. Whether you've been feeling more anxious than normal or sluggish and picking up an extra few pounds, there's no reason not to get tested. Thyroid disease is a slippery fish, but knowing all you can about the little gland is the best place to start.

Expert-approved
READ THIS NEXT: How to Feel Great Even Though You've Gained Weight 34U34 Activism Promo