If you notice your eyebrows getting thinner, it may be time to get your thyroid hormone levels checked out. According to Pouya Shafipour, MD, a board-certified physician with Paloma Health, a thyroid imbalance can cause you to lose eyebrow hair because “thyroid hormones are essential for the development and creation of hair follicles.” When your thyroid is functioning correctly, your hair follicles regenerate by going through phases of growth, regression, shedding, and more growth. However, “when the thyroid is either over-producing or under-producing hormones, your hair follicles may not be stimulated as much as they need to be, resulting in hair loss” from places like the eyebrows, Shafipour explains. And for more on what changes in your hair could mean, check out the 13 Things Your Hair Is Trying to Tell You About Your Health. Hypothyroidism is a condition in which your thyroid is underactive, meaning it does not create enough thyroid hormone. According to David Beatty, MRCGP, a general practitioner with more than 30 years of experience, if you have hypothyroidism, most of the eyebrow hair loss occurs in the outer third part of your brow where it extends toward your ears. Thinning eyebrows in this area are often cited as a unique, early symptom of hypothyroidism.ae0fcc31ae342fd3a1346ebb1f342fcb Other symptoms of an underactive thyroid include dry skin, brittle nails, or weight gain, says Shafipour. And for more clear signs of health issues, If You Notice This on Your Hands, Get Your Liver Checked, Doctors Say. Interestingly, losing eyebrow hair is also a symptom of hyperthyroidism, says Shafipour. If you have hyperthyroidism, that means you have an overactive thyroid that creates too much thyroid hormone. “Hypothyroidism is roughly five times as common as hyperthyroidism,” Beatty notes, so it’s more likely thinning eyebrows are the result of an underactive thyroid. Nevertheless, you’ll want to be aware of what accompanying symptoms to look out for. Other signs of hyperthyroidism include symptoms that “feel like the body is speeding up,” Shafipour says, such as excess sweating, restlessness, or a fast heartbeat. And for more up-to-date information on your health, sign up for our daily newsletter. Fortunately, thyroid-related eyebrow hair loss is typically temporary, according to MedicalNewsToday. Once you treat your condition and your thyroid levels return to normal, your hair should grow back and return to its original fullness. Untreated thyroid disorders lead to other health complications beyond hair loss. Both untreated hypothyroidism and hyperthyroidism can increase your risk of heart failure, according to the Mayo Clinic, while hypothyroidism is specifically linked to slowed mental functioning and hyperthyroidism is linked to vision loss. Both of these thyroid imbalances can also progress into severe states as well if untreated, producing life-threatening conditions like myxedema with hypothyroidism and thyrotoxic crisis with hyperthyroidism. And for more on your thyroid, If You Notice This on Your Nails, Get Your Thyroid Checked, Doctors Say.