Straight eyelashes are mostly determined by genetics and the internal structure of your lash follicles. All human eyelashes have some degree of curvature built into them, but how much curl you actually see varies widely from person to person. If your lashes appear to grow straight out or even point downward, it comes down to the shape of your follicle, the protein structure inside each lash, and your ethnic background.
How Follicle Shape Creates Curl (or Doesn’t)
Eyelash curvature starts deep inside the follicle, at the bulb where the lash begins forming. In people with visibly curled lashes, the internal structure of this bulb is asymmetric: certain sheaths along one side are thicker than on the other. That unevenness forces the lash to bow as it grows, creating a curve from root to tip. When the bulb is more symmetrical, the lash grows out straighter because there’s less mechanical force bending it in one direction.
Inside the lash itself, keratin proteins are held together by chemical connections called disulfide bonds. These bonds aren’t evenly distributed throughout every lash. Areas with denser bonds create rigidity, while areas with fewer bonds allow more flexibility. The specific pattern of bond distribution you’re born with plays a direct role in whether your lashes curl upward or extend straight. People with naturally straight lashes tend to have a more uniform bond arrangement, which means the lash has no structural reason to bend.
Genetics Are the Biggest Factor
Two genes have been identified as major players in hair straightness, and both influence eyelashes along with the hair on your head. A gene called EDAR (specifically a variant known as rs3827760) is the dominant factor in East Asian populations, accounting for a measurable percentage of variation in hair straightness across nearly 3,000 Han Chinese participants in one genome-wide study. A different gene, TCHH (Trichohyalin), is more strongly associated with hair straightness in people of European descent. In mixed populations, both genes contribute independently through separate mechanisms, meaning straight hair traits can come from either genetic pathway.
If your parents or siblings have straight lashes, you very likely inherited the same follicle structure and protein distribution patterns. This is the simplest and most common explanation for straight-growing lashes.
Ethnicity and Lash Angle
Your ethnic background significantly affects how your lashes sit. A comparative study of Asian and Caucasian women found that Asian eyelashes had lower lift-up angles and lower curl-up angles than Caucasian lashes. Asian lashes also tended to be thicker in diameter and had more layers of outer cuticle (about 8 layers versus 6.5 in Caucasian lashes), which adds stiffness and makes the lash more resistant to curling. Interestingly, actual lash length and growth rate were the same between the two groups, so straighter lashes aren’t shorter or slower-growing.
This means that if you’re of East Asian descent, having lashes that grow straight or point slightly downward is completely typical. The thicker, denser structure of each individual lash simply holds its shape more rigidly. Eye makeup, by the way, did not influence lash characteristics in either group in that study, so mascara or liner isn’t reshaping your lashes over time.
When Straight Lashes Are a New Development
If your lashes used to curl and have recently started growing straighter, something other than genetics may be involved. Aging gradually changes hair texture everywhere on your body, including your eyelids. Hormonal shifts during menopause, pregnancy, or thyroid changes can alter the protein composition of new lashes as they grow in, sometimes resulting in lashes that are straighter, finer, or point in a different direction than before.
Blepharitis, a common inflammation of the eyelids caused by bacteria, skin conditions, or certain medications, can also change how lashes grow. People with chronic blepharitis sometimes notice lashes that fall out, thin, or start growing in unusual directions. If your straight lashes are accompanied by redness, flaking, or irritation along the lash line, that’s worth having checked.
Eyelash ptosis is a specific condition where upper lashes develop a downward bend or droop. The most common medical association is with floppy eyelid syndrome, a condition linked to lax eyelid tissue. This is distinct from naturally straight lashes because it represents a change from a previous growth pattern.
The Eyelash Growth Cycle
Each eyelash goes through three phases: active growth lasting about 30 to 45 days, a transition phase of 2 to 3 weeks where the lash reaches its full length and stops growing, and a resting phase of 3 to 4 months before the lash falls out and a new one begins. Only about 18% of your eyelashes are in the active growth phase at any given time. This matters because if you’re trying to change your lash curl with serums or treatments, results take time. A new lash needs to complete its full growth cycle before you can see whether its shape has changed, and that cycle runs roughly 5 to 6 months from start to shed.
What You Can Do About Straight Lashes
Eyelash curlers are the most immediate option. Heated curlers work similarly to curling irons for head hair: they temporarily break some of the hydrogen bonds in the keratin, allowing you to reshape the lash while warm, and the bonds re-form in the new position as the lash cools. The effect lasts until the lash gets wet or the bonds gradually relax back to their natural position.
Lash lift treatments at salons take this a step further by using chemical solutions to temporarily break and reform the stronger disulfide bonds within the lash. This produces a semi-permanent curl that lasts through the natural lifespan of each treated lash, typically 6 to 8 weeks. The process is essentially a perm for your eyelashes. Because the treatment works on the bonds that determine your lash’s resting shape, it’s the closest thing to changing your lash structure without waiting for genetics to do something different.
For lashes that have changed direction due to a medical condition like blepharitis, treating the underlying inflammation often restores more normal lash growth over subsequent cycles. Trichiasis, where otherwise normal lashes misdirect inward toward the eye, is a separate issue that typically needs clinical correction rather than cosmetic treatment.