Almost everyone has one eyebrow slightly lower than the other. A study of 321 young, healthy adults found that measurable facial asymmetry was present in every group examined, with females showing left-right differences in 33% of facial measurements and males in 13%. Even faces considered aesthetically attractive have significant asymmetry, and differences of up to 5 or 6 millimeters between sides fall within normal limits. So if you’ve noticed unevenness in a mirror or photo, the most likely explanation is that your face is simply doing what faces do. But several factors can make the difference more pronounced.
How Your Muscles Control Brow Height
One muscle lifts your eyebrows: the frontalis, a broad sheet of vertical fibers across your forehead. When it contracts, it pulls the skin and brows upward. Working against it are three muscles that pull the brows down: one between your brows that draws them together, one that pulls the inner brow downward, and the circular muscle surrounding each eye socket.
The balance between these lifting and lowering forces determines where each brow sits at rest. If the lifting muscle is slightly stronger or more active on one side, that brow will sit higher. If the depressor muscles are more dominant on one side, that brow drops. This tug-of-war happens independently on each side of your face, and it’s rare for both sides to be perfectly matched.
Habits That Shift Brow Position Over Time
Repetitive facial expressions can gradually change where your brows rest. If you habitually raise one eyebrow when you’re skeptical, concentrating, or talking, the lifting muscle on that side gets more of a workout. Over years, this can create a visible difference in resting brow height. Squinting one eye more than the other, whether from a prescription difference or just a habit, strengthens the depressor muscles on that side and pulls the brow lower.
Sleep position plays a role too. Research published by the Aesthetic Society found that sleeping on your side or stomach causes mechanical compression that distorts facial soft tissue over time. Most of this distortion shows up on the forehead, lips, and cheeks. If you consistently sleep on one side, the sustained pressure can reshape the tissue around that brow differently than the other. Unlike wrinkles caused by muscle movement, these compression-related changes can’t be treated with injections that relax muscles.
How Aging Makes the Difference Worse
If your eyebrows were always slightly uneven, aging tends to amplify the gap. Several things happen at once. Collagen breaks down faster than your body replaces it. Around age 40 to 50, your skin’s elastic fibers begin declining steeply, and the skin loses its ability to snap back into place. Fat pads in the forehead that once provided structural support start to shrink or slide downward, and the lateral brow in particular can sag from the weight of descending fat pads above it.
Bone changes matter too. The rim of the eye socket gradually recedes with age, removing the bony shelf that helped hold the brow in position. Without that support, the brow drops below where the rim used to be. Since aging rarely progresses at the same rate on both sides of the face, the brow that was already slightly lower often drops further and faster, making what was once a subtle difference much more noticeable.
Medical Conditions That Cause Sudden Drooping
A brow that drops noticeably over days or weeks, rather than years, can signal a medical problem. Bell’s palsy, which temporarily paralyzes the nerve controlling one side of the face, is one of the most common causes. With Bell’s palsy, you’ll have trouble closing the eye, smiling, and raising the brow on the affected side. It typically resolves on its own over weeks to months.
A stroke can also cause one-sided facial drooping, but it looks different. Stroke-related drooping usually affects the lower face more than the forehead, and it comes with other symptoms: difficulty finding words, vision changes, trouble walking, or weakness in an arm or leg. Bell’s palsy never causes arm or leg weakness or difficulty moving the eyes or tongue. If facial drooping appears suddenly alongside any of those other symptoms, that’s a medical emergency.
Other conditions that affect nerve or muscle function can cause one brow to drop gradually. Autoimmune conditions that weaken the connection between nerves and muscles sometimes show up first around the eyes as fatigue-related drooping that worsens throughout the day.
Drooping Brow vs. Drooping Eyelid
Many people assume they have a drooping eyelid when the real issue is a drooping brow. The distinction matters because treatments are different. A simple test helps sort it out: if you gently lift the brow to where it should sit and the heavy, hooded appearance goes away, the problem is brow position. If the eyelid still hangs low even with the brow lifted, the eyelid itself has a separate issue called blepharoptosis.
Sometimes both problems exist together. In some cases, a drooping eyelid on one side actually pulls the brow down with it, creating a cycle where brow and lid droop reinforce each other. There’s also a quirk of how your brain wires both eyes together: if one eyelid is propped open more than normal (by lifting it or the brow above it), the opposite eyelid can reflexively droop. This means some people actually have asymmetry on both sides that only becomes apparent when one side is corrected.
Correcting Uneven Brows Without Surgery
Neuromodulator injections (commonly known by brand names like Botox) are the most popular non-surgical option for balancing brow height. The basic principle is straightforward: relax the muscles pulling the lower brow down, and it rises. A typical approach involves small doses injected into the depressor muscles between the brows and just beneath the brow on the lower side. Doses are kept small in these areas, often just a few units per injection point, to avoid a frozen or surprised look.
For brows that need more lift than muscle relaxation alone can provide, a small amount of dermal filler placed under the brow can physically prop it into a higher position. This requires very little product, typically a fraction of a milliliter, and extends the results beyond what injections alone achieve. Results from neuromodulators last roughly three to four months, while filler can last longer depending on the product used.
Surgical Options for Significant Asymmetry
When the difference between brows is large, or when nerve damage has permanently weakened one side, surgery offers more lasting correction. Several techniques exist, and the choice depends on how much lift is needed and where.
- Direct brow lift: An incision is made just above the brow, allowing precise repositioning of one side independently. This is particularly useful for people with facial paralysis because it gives the surgeon exact control over how much each brow moves.
- Endoscopic brow lift: Several small incisions are hidden within the hairline, and a tiny camera guides the surgeon in releasing and repositioning the tissue. This is the most common approach for age-related brow descent and leaves minimal visible scarring.
- Hairline or coronal brow lift: Incisions are placed at or behind the hairline for broader lifting across the entire forehead. These are better suited for people who need correction on both sides.
The trend in recent years has moved toward minimally invasive endoscopic techniques for most patients, with direct brow lifts reserved for cases where one-sided precision is the priority. Recovery from endoscopic procedures typically involves swelling and bruising for one to two weeks, with final results settling over several months as the tissue heals into its new position.