Lines in or around the eyebrows can mean several different things depending on what you’re seeing. Some lines are wrinkles etched into the skin between your brows, others are streaks of missing hair, and some are deliberate style choices shaved into the brow. Each has a distinct cause, and knowing the difference helps you figure out whether what you’re noticing is cosmetic, medical, or purely intentional.
Vertical Lines Between the Eyebrows
The most common “lines in eyebrows” people notice are the vertical creases that form between the brows, often called frown lines or “11 lines” because they look like the number eleven. These are caused by a small muscle called the corrugator supercilii, which contracts every time you squint, concentrate, or frown. Over years of repeated use, the skin above that muscle develops permanent furrows that stay visible even when your face is relaxed.
Aging accelerates the process. As skin gets older, its collagen matrix starts to fragment. Collagen is the structural protein that keeps skin firm and bouncy. Specific enzymes break it down over time, and once enough collagen is lost, the cells responsible for producing new collagen can no longer attach properly. They collapse and start producing even less collagen while generating more of the enzymes that destroy it. This creates a self-reinforcing cycle: the skin gets thinner and less elastic, and those once-temporary expression lines become permanent grooves. Sun exposure, smoking, and dehydration speed this up considerably.
For people bothered by deep frown lines, injectable treatments that relax the underlying muscle are the most common solution. The effect typically lasts about three to four months before the muscle regains activity and the lines gradually return. Topical retinoids and sunscreen can slow further collagen loss but won’t erase deep creases on their own.
Lines of Hair Loss in the Brow
If the “lines” you’re seeing are actually gaps, thin patches, or streaks where hair is missing, that points to a different set of causes. The medical term for eyebrow hair loss is madarosis, and it ranges from subtle thinning to complete loss of sections of the brow.
Thinning at the Outer Third
One specific pattern worth knowing about: losing hair on the outer third of the eyebrow, the section closest to your ears. This is called Hertoghe’s sign, and it’s a classic indicator of hypothyroidism, where the thyroid gland isn’t producing enough hormones. If you notice your eyebrows seem to be disappearing from the outside in, it’s worth getting your thyroid levels checked. The hair often grows back once thyroid function is corrected with medication.
Patchy or Irregular Loss
Autoimmune conditions can also attack eyebrow hair. Alopecia areata creates smooth, well-defined patches of hair loss that can appear anywhere on the body, including the brows. Lupus, scleroderma, and sarcoidosis are other autoimmune diseases that sometimes cause brow thinning. These conditions typically come with additional symptoms beyond hair loss, such as fatigue, joint pain, or skin changes elsewhere on the body.
Trichotillomania, a condition where a person repeatedly pulls out their own hair (sometimes without realizing it), can also create noticeable lines or gaps in the eyebrows. The pattern of loss tends to look uneven and may be more prominent on the dominant-hand side.
Chemotherapy, radiation therapy, and certain prescription medications can cause temporary eyebrow loss as well. In most of these cases, the hair returns after treatment ends, though regrowth can take several months.
Flaky or Red Lines Through the Brows
Sometimes the lines people notice aren’t about hair loss or wrinkles at all. They’re patches of flaky, scaly, or reddened skin running through the brow area. The eyebrows sit in an oily zone of the face, which makes them a prime target for seborrheic dermatitis. This condition produces oily patches covered in yellow or white scales, along with itchiness and flaking. It commonly affects the eyebrows, the sides of the nose, the ears, and the scalp (where it’s simply called dandruff).
Psoriasis, eczema, and contact dermatitis can produce similar-looking irritation in the brow area. If the flaking is persistent and doesn’t respond to basic moisturizing, a medicated shampoo or topical antifungal applied to the brow area often helps with seborrheic dermatitis specifically. The condition tends to come and go in flares rather than resolving permanently.
Intentional Eyebrow Slits
Not all lines in eyebrows signal a health issue. Eyebrow slits, where one or more thin lines are shaved into the brow, are a deliberate fashion choice with roots in 1980s and 1990s hip-hop culture. The look carried a rebellious, tough-guy edge. The slit was thought to suggest a scar from a fight, and over the years it became loosely associated with gang affiliation in some communities.
Today, eyebrow slits carry no particular connotation beyond personal style. The trend has cycled back into mainstream popularity, partly inspired by celebrities. Actor Jason Momoa sports a genuine scar through his eyebrow from being cut with a broken glass, and the character Maze in the series Lucifer (played by Lesley-Ann Brandt) prominently featured the look. Single slits, double slits, and angled cuts are all common variations. Unlike the other causes on this list, eyebrow slits are purely cosmetic and the hair grows back within a few weeks if left alone.
How to Tell What Your Lines Mean
A quick way to narrow things down: look at whether the lines involve the skin, the hair, or both. Vertical creases in the skin between your brows, especially ones that deepen when you frown, are expression lines driven by muscle movement and aging. Gaps where hair used to be, particularly at the outer edges, point toward a medical cause like thyroid dysfunction or an autoimmune condition. Flaky, scaly patches suggest a skin condition like seborrheic dermatitis. And clean, precise lines shaved into otherwise full brows are a style choice.
If your eyebrow hair is thinning gradually and you can’t pinpoint a reason, pay attention to other changes in your body. Fatigue, weight gain, dry skin, and feeling cold all the time alongside outer-brow thinning is a pattern that strongly suggests hypothyroidism. Sudden patchy loss without other symptoms is more typical of alopecia areata. And if the skin itself is the problem, with redness, scaling, or itching concentrated in the brow area, a targeted skin treatment is usually all that’s needed.