Eyebrow hair falls out for a wide range of reasons, from nutrient shortfalls and hormonal shifts to autoimmune conditions and skin infections. Sometimes the cause is as simple as years of overplucking; other times it signals something happening inside your body that deserves attention. Understanding the pattern of loss, where on the brow it’s happening, and what other symptoms accompany it can help narrow down the cause.
How Eyebrow Hair Grows (and Sheds)
Eyebrow hairs have a much shorter active growth phase than the hair on your head. Each brow follicle grows for only about two to three months before entering a resting phase that lasts another two to three months. During that resting phase, the old hair eventually falls out and a new one begins growing in its place. Because the growth window is so brief, eyebrow hairs stay short, and any disruption to the cycle is noticeable quickly. It also means that when the underlying cause is corrected, regrowth can take several months to become visible.
Thyroid Problems and the Outer Eyebrow
One of the most recognizable patterns of eyebrow loss is thinning that starts at the outer third of the brow, sometimes called the Hertoghe sign. This pattern is strongly associated with an underactive thyroid. Your thyroid gland produces hormones that regulate many processes in the body, including hair growth. When thyroid hormone levels drop, a buildup of certain compounds between cells can trigger low-grade inflammation in the skin, which disrupts the follicle’s ability to hold onto hair.
Another theory is that hypothyroidism interferes with the autonomic nervous system, the network of nerves responsible for unconscious processes like blood flow to hair follicles. Either way, if you notice your eyebrows thinning specifically from the tail end inward, a simple blood test for thyroid function is a logical first step.
Alopecia Areata
Alopecia areata is an autoimmune condition in which your immune system mistakenly attacks hair follicles. It can affect the scalp, eyebrows, eyelashes, or any combination. Eyebrow loss from alopecia areata often appears as one or more smooth, well-defined patches where hair is completely absent, rather than a gradual thinning. The condition is unpredictable: hair may regrow on its own, fall out again, or remain stable for long stretches.
Frontal Fibrosing Alopecia
Frontal fibrosing alopecia (FFA) is a scarring form of hair loss that most commonly affects postmenopausal women, though it can occur in men and younger women too. A key feature of FFA is that eyebrow loss often appears before any noticeable thinning along the hairline. The immune system attacks the follicle and replaces it with scar tissue, which means the loss can become permanent if left untreated. If your eyebrows are disappearing and your hairline also seems to be creeping back, FFA is worth investigating with a dermatologist.
Nutrient Deficiencies
Your hair follicles need a steady supply of certain nutrients to stay in their growth phase. When those nutrients run low, follicles can shift prematurely into the resting phase, causing noticeable shedding.
Iron is the most common nutritional deficiency worldwide and a well-established cause of diffuse hair loss, including in the brows. Iron-deficiency anemia starves follicles of the oxygen they need to produce hair. Vegans, vegetarians, people with heavy menstrual periods, and those with absorption issues are at higher risk.
Zinc plays a role in follicle structure and cell division. Studies comparing people with various forms of hair loss to healthy controls have found significantly lower zinc levels in the hair-loss group. Low zinc can also make existing hairs brittle and prone to breakage.
Biotin deficiency, while relatively rare, causes a characteristic combination of hair loss and a scaly skin rash. People who regularly consume raw egg whites are at risk because a protein in raw whites binds to biotin and prevents absorption.
Seborrheic Dermatitis
The eyebrow area is rich in oil glands, which makes it a common site for seborrheic dermatitis. This condition involves overproduction of skin oil combined with an overgrowth of a yeast that naturally lives on your skin. Together, they create flaky, inflamed patches that itch. The inflammation itself can damage follicles and push hairs out prematurely, and scratching makes things worse by physically disrupting the follicle.
The good news is that hair lost to seborrheic dermatitis typically grows back once the inflammation is controlled. Treatment usually involves antifungal and anti-inflammatory topicals applied directly to the brow area.
Fungal Infections
A fungal infection of the face can target eyebrow hair directly. Unlike seborrheic dermatitis, which involves a yeast already on your skin, these infections are caused by dermatophyte fungi, sometimes picked up from pets like cats or guinea pigs. The fungus invades the hair shaft itself, causing hairs to break off at the surface or fall out entirely. You might notice redness, slight scaling, or crusting around the affected area. Interestingly, only a minority of cases show the classic ring-shaped rash people associate with “ringworm,” which can make it easy to misdiagnose as something else. A skin scraping can confirm whether a fungal infection is responsible.
Stress-Related Shedding
A condition called telogen effluvium can push large numbers of hair follicles into their resting phase simultaneously. Triggers include severe illness, surgery, high fever, significant emotional stress, crash dieting, or hormonal changes like childbirth. The hallmark timing is a delay of about three months between the triggering event and the onset of noticeable shedding. So if your eyebrows started thinning seemingly out of nowhere, think back to what was happening in your life roughly three months earlier.
Telogen effluvium is almost always temporary. Once the trigger resolves, follicles re-enter their growth phase and hair fills back in over the following months.
Overplucking and Physical Damage
Repeated plucking, waxing, or threading over many years can eventually cause permanent damage. In the early stages, the follicle recovers and produces a new hair each time. But chronic trauma triggers a process where the follicle is gradually replaced by scar tissue. Once scarring sets in, the follicle loses its ability to regenerate. This is the same mechanism behind traction alopecia on the scalp. If you’ve been aggressively shaping your brows for years and notice that some areas no longer fill in, those follicles may have crossed the threshold into permanent loss.
When Eyebrows Can Grow Back
Regrowth depends entirely on whether the follicle is still alive. Conditions that cause inflammation without scarring, like seborrheic dermatitis, telogen effluvium, nutrient deficiencies, and treated thyroid disease, generally allow full regrowth once the underlying problem is addressed. Scarring conditions like frontal fibrosing alopecia and late-stage traction damage are a different story: once scar tissue replaces the follicle, that hair is gone for good.
For people looking to speed up regrowth or improve brow fullness, a prescription solution originally developed for eyelash growth has shown promise. In a clinical trial, about 80% of participants using this treatment daily saw measurable improvement in eyebrow fullness, with visible changes starting around month two. Eyebrow darkness improved even sooner, within the first month.
Because the eyebrow growth cycle is short, you can generally expect to see whether a treatment is working within three to four months. If your brows are thinning and you’re not sure why, the pattern of loss is one of the most useful clues: outer-third thinning points toward the thyroid, smooth bare patches suggest an autoimmune cause, flaky irritated skin implicates dermatitis or infection, and diffuse thinning across both brows raises the question of nutrition or stress.