Latisse works by extending the active growth phase of your eyelash hair follicles, resulting in lashes that are longer, thicker, and darker than they would naturally grow. The active ingredient, bimatoprost, was originally developed to treat glaucoma and was approved by the FDA in December 2008 specifically for eyelash growth after doctors noticed patients on the eye-pressure drug were developing noticeably fuller lashes.
How Bimatoprost Changes the Hair Growth Cycle
Every eyelash follicle cycles through three phases: a growth phase (anagen), a transition phase, and a resting phase before the lash eventually falls out and is replaced. At any given time, your lashes are all at different points in this cycle, which is why you don’t lose them all at once. Bimatoprost increases the percentage of follicles that are actively growing at the same time. Since lashes only get longer while they’re in the growth phase, keeping more follicles in that window for a longer stretch means noticeably longer lashes overall.
The drug also affects the follicle structure itself. It enlarges the dermal papilla and hair bulb, which are the parts of the follicle responsible for producing the hair shaft. Larger structures produce thicker individual lashes. At the same time, bimatoprost stimulates melanin production inside the follicle, which is the pigment that gives hair its color. This is why treated lashes tend to look darker, not just longer. In clinical trials, treated lashes grew an average of 1.4 mm longer than baseline, roughly a 25% increase in length.
How to Apply It
Latisse is applied once nightly, using a sterile disposable applicator. You place a single drop of the solution onto the applicator and brush it along the skin of your upper eyelid margin, right at the base of your lashes. Only the upper lash line gets treated. The lower lashes typically pick up enough of the solution through natural blinking and contact, and direct application to the lower lid increases the risk of the solution spreading to areas where you don’t want it.
After applying, blot any excess solution with a tissue so it doesn’t run down your cheek or pool around your eye. Extra product on surrounding skin won’t make lashes grow faster, but it can cause unwanted pigmentation changes or irritation in those areas. Use a fresh applicator for each eye to keep things sterile.
Timeline for Visible Results
Most people start noticing changes in lash length around week four. This makes sense biologically: the follicles need time to shift into a prolonged growth phase and for that new growth to become visible. The changes are gradual, so day-to-day differences are subtle.
Full results typically appear around week 16, or about four months of consistent nightly use. At that point, you’re seeing the cumulative effect of a higher proportion of follicles actively growing, producing thicker and darker hairs simultaneously. Skipping nights or using it inconsistently will slow this timeline, since the drug needs to keep influencing the follicle cycle without interruption.
What Happens When You Stop
Latisse doesn’t permanently change your lash follicles. Once you stop applying it, your eyelashes gradually return to their original length, thickness, and color as follicles cycle back to their natural rhythm. This reversal takes anywhere from three to 24 weeks, depending on where individual follicles are in their growth cycle when you discontinue. Some people maintain their results by reducing application to every other night or a few times a week, though the prescribing information is based on nightly use.
Side Effects Worth Knowing About
The most common side effects are mild: redness or itchiness at the application site, which often resolves as your skin adjusts. But bimatoprost belongs to a class of drugs called prostaglandin analogs, and these carry some less obvious risks that are worth understanding before you start.
Skin Darkening Around the Eyes
Bimatoprost can darken the skin of your eyelids and the area immediately around your eyes. This is the same melanin-stimulating effect that makes lashes darker, just happening in skin you didn’t intend to treat. Careful application and blotting excess solution significantly reduces this risk. The darkening typically fades after stopping treatment.
Changes to Eye Socket Appearance
Prostaglandin analogs can cause a condition called prostaglandin-associated periorbitopathy, which involves fat loss around the eye socket. Symptoms include a deepening of the crease above the upper eyelid, a sunken appearance to the eyes, and changes in how the eyelid sits. These effects appear anywhere from several weeks to several years after starting treatment. Biopsies of orbital fat in patients using prostaglandin analogs show that the fat cells shrink in size, and bimatoprost has the most pronounced effect on fat cell density compared to related drugs. These changes can improve after discontinuing the medication, though recovery varies.
Iris Color Change
The most unusual potential side effect is a permanent darkening of the iris, the colored part of your eye. This has been most extensively studied in glaucoma patients using related prostaglandin drugs as eye drops (applied directly into the eye, not just on the lash line). In those populations, reported rates of iris darkening range from about 11% to 23% depending on the study, with the risk being highest in people with mixed-color irises (hazel or green-brown). The risk with Latisse is considered lower because the solution is applied to the skin rather than dropped into the eye, limiting how much reaches internal eye tissues. Still, if you have light or mixed-color eyes, this is a side effect to be aware of. Any color change that does occur is likely permanent.
Why It Only Works While You Use It
Bimatoprost doesn’t reprogram your follicles or create new ones. It temporarily overrides the natural timing signals that tell a follicle to stop growing and start resting. Think of it like keeping a light on longer rather than installing a brighter bulb. The moment you remove the signal, the follicle defaults back to its genetically determined cycle length. This is why Latisse is an ongoing commitment rather than a one-time treatment. The lashes you grow while using it are real, fully your own lashes, just coaxed into a longer and more productive growth phase than they’d manage on their own.