Thinning Outer Eyebrows and Your Thyroid: What an Endocrinologist Looks For

Picture each eyebrow in three parts: the head near the nose, the arch, and the tail that tapers toward the temple. The tail, or outer third, is where thinning tends to show first. Brow hair grows in cycles just as scalp hair does, with a growing phase, a resting phase and a shedding phase. When something shortens the growing phase or slows the follicle, the fine hairs at the tail are often the first to go, and the brow can look shorter or less defined.

Loss of hair at the outer third of the eyebrow is a classic sign associated with an underactive thyroid, also called hypothyroidism. Thyroid hormones help set the pace of the hair growth cycle. When levels run low, follicles can spend less time growing and more time resting, and hair may become sparse, dry or brittle.

It is a clue, not a diagnosis. Many people with an underactive thyroid never notice brow changes, and many people with thinning brows have normal thyroid function. Other features that can be associated with an underactive thyroid include fatigue, feeling cold, dry skin, weight change, constipation and thinning scalp hair. If several of these sound familiar, talk with your physician.

The outer brow can thin for many reasons, and more than one can be present at the same time:

• Aging. Brow hair naturally becomes finer and sparser over time, and growth slows.
• Overplucking or waxing. Years of shaping can damage follicles so hairs grow back thinner or not at all.
• Perimenopause and menopause. Falling estrogen can shift the hair growth cycle in the brows as well as the scalp.
• Iron and nutrient issues. Low iron stores, low vitamin D and low protein intake can be associated with hair thinning.
• Alopecia areata. This autoimmune condition can cause patchy hair loss in the brows, lashes or scalp.
• Eczema and other skin conditions. Inflammation, itching and rubbing around the brows can lead to breakage and shedding.

It is tempting to reach for a brow serum, tinting or microblading. Those can be reasonable choices, but they only change how the brow looks. If an underactive thyroid, low iron or another medical cause is driving the change, it continues underneath, and it may be affecting your energy, skin and scalp hair too.

A medical review usually starts with your history: when the thinning began, whether it affects both sides, how you shape your brows, your medications, any recent illness or weight change, and any family history of thyroid or autoimmune disease. Your physician may suggest blood tests, which commonly include thyroid function and iron studies. The results guide what comes next, whether that is medical care, a cosmetic plan, or both.

Thyroid eye disease is a separate condition, most often linked with Graves' disease, an autoimmune condition that makes the thyroid overactive. It can affect the muscles and soft tissue around the eyes. Some people notice eyelids that sit higher or pull back, puffiness, a staring look, dryness, redness or eyes that appear more prominent.

These changes alter how the brow and lids sit, so they matter for any treatment planned around the eyes. New eye symptoms such as double vision, eye pain or changes in vision need prompt medical attention. Talk with your physician or an eye specialist before considering cosmetic care in that area.

Dr. Anna Frisch, MD, PhD, is Board Certified in Endocrinology. At Palm Beach Cosmetic Medicine she practices Aesthetic Endocrinology, which means a brow concern is looked at through the lens of endocrinology before any cosmetic plan is made. Many brow changes are purely cosmetic, and the plan reflects that. Some can be associated with a hormonal cause, and her training helps her recognize which is which.

If your history suggests a thyroid or hormone question, evaluation and treatment take place at Palm Beach Thyroid, Endocrinology & Wellness in person or through Frisch Integrative Medicine by telemedicine, not at PBCM. When the concern is cosmetic, such as a brow that has started to sit lower, PBCM can plan care around your anatomy, your thyroid history and any eye findings.

Learn how hormone science shapes cosmetic planning on the Aesthetic Endocrinology page, or read about the non-surgical brow lift at PBCM in Wellington. If you have noticed outer brow thinning along with other symptoms, talk with your physician about whether testing makes sense for you.