The vertical lines between your eyebrows, often called “11 lines” or glabellar lines, are caused by repeated contraction of two small muscles that pull your brows inward and downward. Over years of frowning, squinting, concentrating, and staring at screens, these muscles can remain partially shortened even when your face is relaxed, creasing the skin above them into permanent grooves. But muscle activity is only part of the story. The lines become fixed because aging skin loses its ability to bounce back.
The Muscles Behind the Lines
Two muscles do most of the work. The corrugator supercilii sits above each eyebrow and pulls the brows toward the center of your face. The procerus runs vertically along the bridge of your nose and pulls the skin between your brows downward. Every time you squint at a bright window, concentrate on a spreadsheet, or furrow your brow in frustration, these muscles fire together.
In your twenties and thirties, the skin smooths out the moment you relax your face. But with enough repetition, the muscles begin to hold residual tension even at rest. Think of it like a piece of paper that’s been folded along the same crease thousands of times. Eventually the fold stays whether you’re pressing on it or not. That constant low-level contraction is what turns a temporary expression into a permanent line.
Why Skin Stops Bouncing Back
Young skin contains dense networks of collagen (the protein that gives skin structure) and elastin (the protein that lets it snap back into place). Starting in your thirties and accelerating through your forties and fifties, your body produces less of both. At the same time, enzymes that break down these proteins become more active. The result is skin that’s thinner, less elastic, and more easily creased by the muscles underneath.
UV exposure speeds this process significantly. Sunlight damages collagen fibers deep in the skin, and while the body repairs some of the damage, the replacement fibers form unevenly, creating a weaker, lumpier foundation beneath the surface. This is why people with years of unprotected sun exposure often develop deeper 11 lines earlier than those who’ve been consistent about sun protection.
High blood sugar also plays a role through a process called glycation. When collagen fibers are exposed to excess glucose over time, they become stiff and brittle rather than flexible. This makes the skin less forgiving of repeated folding, so expression lines set in faster.
Bone Changes Add to the Problem
Most people don’t realize that the skull itself changes shape with age. The eye sockets gradually enlarge, averaging 15 to 20 percent larger by your sixties and seventies, and the bone around the brow and midface slowly resorbs. This means the scaffolding underneath your skin is shrinking, leaving more slack tissue to fold and crease. It’s one reason 11 lines tend to deepen noticeably in middle age even if your habits haven’t changed.
Habits That Make 11 Lines Worse
Anything that makes you recruit those brow muscles more often will deepen the lines faster. Common culprits include:
- Screen time. Hours of staring at a computer or phone often involves unconscious squinting and brow furrowing, especially if your screen brightness or text size isn’t optimized.
- Uncorrected vision. If you need glasses or a stronger prescription, you’re likely squinting throughout the day without realizing it.
- Sun glare. Forgetting sunglasses on bright days forces constant squinting. The American Society for Dermatologic Surgery specifically recommends sunglasses as a preventive measure for frown lines.
- Stress and poor sleep. Chronic stress keeps facial muscles tense, and sleep deprivation compounds the effect. Both increase the baseline level of muscle contraction in the brow area.
- Smoking. Nicotine constricts blood vessels and reduces oxygen delivery to the skin. Skin cells need adequate oxygen to produce collagen, and smoking directly inhibits the synthesis of the two main types (type I and type III) while ramping up the enzymes that break collagen down. Research on women’s skin found that smokers in their fifties had significantly less type I collagen in their skin compared to nonsmokers of the same age. Smoking also generates oxidative stress that further degrades elastic fibers.
How Severity Is Measured
Dermatologists classify 11 lines on a simple four-point scale. At grade 0, no lines are visible. Grade 1 (mild) means lines appear when you frown but mostly disappear at rest. Grade 2 (moderate) means lines are clearly visible and their depth can be gauged just by looking at the surface. Grade 3 (severe) means deep, clearly visible furrows whose depth can’t be assessed from the surface alone. Most people start seeking treatment at moderate to severe, though many notice mild lines years earlier.
The shift from “lines that appear when I frown” to “lines that are there all the time” is what distinguishes dynamic wrinkles from static ones. Dynamic lines are purely a muscle issue. Static lines mean the skin itself has been permanently creased. Most people dealing with noticeable 11 lines have a combination of both.
Treatment Options
The most common treatment is a neurotoxin injection (brands include Botox, Dysport, and Xeomin). These work by temporarily relaxing the corrugator and procerus muscles so they stop creasing the skin. A typical session involves five small injections in the brow area and takes a few minutes. Results usually appear within a week and last three to four months before the muscles gradually regain activity. Because each brand uses different formulations, doses aren’t interchangeable, so switching brands isn’t as simple as matching numbers.
For lines that remain visible even when the muscles are relaxed, dermal fillers can be placed beneath the crease to lift it from underneath. Some practitioners combine both approaches: neurotoxin to stop the muscle from deepening the line, and filler to smooth what’s already etched in.
What Topical Products Can Do
Topical options work more slowly and modestly than injections, but they can help, particularly for mild lines. Retinoids (vitamin A derivatives) stimulate collagen production over months of consistent use and are the best-studied topical for wrinkle reduction. Peptide-based creams take several approaches: some signal skin cells to produce more collagen, elastin, and hyaluronic acid; others mimic the muscle-relaxing effect of neurotoxins on a smaller scale. One clinical study on a topical peptide called Argireline found nearly 49 percent improvement in wrinkle appearance, though results vary widely between products and individuals.
A meta-analysis in Frontiers in Medicine found that topical peptides as a category produced modest wrinkle reduction that didn’t reach statistical significance, while oral collagen peptides showed a stronger, measurable effect. In practical terms, a good topical can soften early lines and slow progression, but it’s unlikely to erase deep, established 11 lines on its own.
Daily sunscreen remains the single most impactful preventive measure. Because UV damage is cumulative and never fully repaired, consistent protection from your twenties onward makes a meaningful difference in how early and how deeply these lines develop.