All human eyelashes are naturally curved, regardless of ethnicity. The curl is built into the structure of each lash from the moment it starts growing inside the follicle. If your lashes seem especially curly compared to other people’s, that comes down to the shape of your follicle, the way proteins are distributed inside each lash fiber, and your genetics.
How Follicle Shape Creates the Curl
Every eyelash gets its curve from an asymmetry that starts deep in the hair follicle, at the bulb where the lash begins forming. The inner layers of tissue surrounding the lash are thicker on one side of the bulb than the other. This lopsided structure forces the lash to bend as it grows upward, and that curvature continues from the root all the way to the tip.
The lash fiber itself is also asymmetric. In curly hair of any kind, a specific structural protein accumulates heavily on the concave (inner curve) side of the shaft, while it’s spread evenly in straighter fibers. This uneven protein distribution essentially “programs” the curl into the lash like a shape memory material. The more pronounced that asymmetry is in your follicles, the curlier your lashes will be. Researchers have confirmed this mechanism holds true across all ethnic backgrounds.
Genetics Determine How Much Curl You Get
The degree of curl in any hair, including lashes, is a complex genetic trait. No single gene flips a switch between straight and curly. Instead, many genes each contribute a small effect. Genome-wide studies have identified three key players: a gene for a protein called trichohyalin (which helps shape the inner root sheath of the follicle), a gene involved in copper transport, and a gene for a specific component of the inner root sheath lining. Variations in these genes influence how symmetrical or asymmetrical your follicle structure ends up being.
Because so many genes are involved, lash curl exists on a spectrum. You might have noticeably curlier lashes than a sibling even though you share most of the same DNA, simply because you inherited a slightly different combination of these small-effect variants. If both your parents have distinctly curly lashes, you’re more likely to as well, but the inheritance pattern isn’t as simple as eye color.
Why Hormones Don’t Change Your Lashes
If you’ve noticed your scalp hair or body hair change texture during puberty, pregnancy, or menopause, you might wonder whether the same thing happens to your lashes. It generally doesn’t. Eyelash follicles are not influenced by androgens, the hormones responsible for transforming fine body hair into thicker, curlier terminal hair during puberty. That’s why lashes stay relatively consistent throughout your life while hair on your legs, underarms, and scalp can shift dramatically with hormonal changes.
During pregnancy, higher estrogen levels can make scalp hair thicker and delay shedding, but eyelashes operate on a much shorter and independent growth cycle. Each lash spends only one to two months actively growing, followed by a two-to-three-week transition period, then a resting phase of two to three months before it falls out and a new one begins. This rapid turnover means lashes don’t accumulate the same hormonal effects that longer-lived scalp hairs do.
The Protective Purpose of Curved Lashes
Your lash curl isn’t just cosmetic. It serves a real aerodynamic function. Wind tunnel experiments have shown that eyelashes act as a passive dust-control system, reducing both airborne particle deposits and tear film evaporation by up to 50%. The optimal lash length for this protection is roughly one-third the width of the eye opening, which is remarkably consistent across mammals.
Interestingly, lash curvature plays a specific role in how air moves around the eye. The natural curve directs a small amount of airflow toward the eye’s surface, which helps maintain a thin boundary layer of still air that keeps dust and debris from settling. Extremely curved lashes, like those on theatrical false lash strips, can actually redirect too much air toward the eye and increase evaporation, reducing the protective effect. Your natural curl is tuned to strike a balance.
When Curly Lashes Become a Problem
For most people, naturally curly lashes are completely harmless and even desirable. But there are two situations where lash direction becomes a medical concern. Trichiasis is a condition where normal lashes grow inward, toward the eye, instead of curving away from it. This causes the lash tips to scrape against the cornea, leading to redness, tearing, irritation, and in severe cases corneal scratches or ulcers. A related condition called entropion involves the entire eyelid turning inward, pressing both skin and lashes against the eye.
These are distinct from simply having curly lashes. If your lashes curl outward and upward (even dramatically so), that’s normal variation. If you feel a scratching sensation, notice persistent redness along the waterline, or can see individual lashes pointing directly at your eyeball, that’s worth getting checked.
Medications That Can Change Lash Curl
If your lashes have recently become noticeably curlier, longer, or thicker and this is a new change, certain medications could be the cause. Prostaglandin-based eye drops, commonly prescribed for glaucoma, are the most frequent culprit. These drops stimulate lash growth and can increase length, curl, and pigmentation. Some cancer treatments that target specific growth factor receptors also cause lash changes, as can immunosuppressants, certain anti-seizure medications, and even some blood pressure drugs.
The clinical term for excessive lash growth is trichomegaly, defined as lashes reaching 12 millimeters or longer with increased curl, thickness, or pigmentation. If your lashes have always been curly, this likely doesn’t apply to you. But if the change is sudden or dramatic, reviewing your medication list is a reasonable first step.