Thicker eyelashes come down to two things: getting more lashes into their active growth phase at once, and preventing the ones you have from breaking or falling out prematurely. Each eyelash cycles through growth, transition, and rest phases independently, which is why you never lose all your lashes at the same time. The active growth phase lasts only 30 to 45 days, followed by a two-to-three-week transition and then about 100 days of rest before the lash sheds. Anything that extends that growth window or protects lashes during it will make them look fuller.
Prescription Serums: The Strongest Option
Bimatoprost (sold as Latisse) is the only FDA-approved product for lengthening, thickening, and darkening eyelashes. It works by increasing the percentage of lash follicles in their active growth phase at any given time, which means more of your lashes are growing simultaneously instead of resting. It also enlarges the base of each hair follicle, directly increasing thickness, and stimulates pigment production so lashes appear darker.
Results aren’t instant. Most people notice subtle changes around weeks four to five, with real fullness and length appearing by weeks six to seven. The best results typically show up between weeks 12 and 16 of consistent nightly use. You apply it along the upper lash line with a thin applicator, and you need to keep using it to maintain results. Once you stop, lashes gradually return to their baseline.
Side effects are relatively uncommon. About 3 to 4 percent of Latisse users experience mild issues. The main concerns are darkening of the eyelid skin, increased iris pigmentation if the solution gets into the eye, and a sunken appearance around the eyes from fat cell shrinkage. The skin darkening and sunken look are generally reversible after stopping use. Iris color changes may not be. Because it’s a prescription, you’ll need to talk with a doctor or eye care provider to get it.
Over-the-Counter Lash Serums
Dozens of non-prescription serums claim to boost lash growth, and they fall into two broad categories: those containing prostaglandin analogs and those built around peptides.
Many popular OTC serums use isopropyl cloprostenate, a prostaglandin analog similar to the active ingredient in Latisse. It’s worth knowing that this ingredient is not FDA-approved for lash growth, and the same potential side effects apply (skin darkening, fat loss around the eyes) without the same level of clinical testing behind it. Controlled trials assessing how often these side effects occur with OTC formulas simply don’t exist yet.
Peptide-based serums take a different approach. Ingredients like myristoyl pentapeptide-17 and myristoyl hexapeptide-16 stimulate keratin production, the structural protein that makes up each lash. In one 90-day clinical study of 29 participants using a peptide-based serum, researchers measured a 35 percent improvement in lash thickness and a 10.5 percent increase in length compared to baseline. Improvements in thickness were statistically significant after just 30 days of daily use. These serums carry fewer risks than prostaglandin-based options, though the results tend to be more modest.
Why Castor Oil Won’t Grow New Lashes
Castor oil is one of the most popular home remedies for eyelash growth, but no scientific evidence supports the claim that it makes lashes grow longer or thicker. What it can do is make existing lashes look better. Castor oil is about 90 percent ricinoleic acid, a fatty acid rich in triglycerides that coats and moisturizes each lash. A 2003 study found it increased hair “luster,” giving a glossier, fuller appearance without changing actual growth. If you want a low-cost way to make your lashes look healthier while you wait for a serum to work, castor oil is a reasonable cosmetic aid. Just don’t expect new growth from it.
Habits That Thin Your Lashes
Before adding products, it helps to stop doing the things that cause lash loss in the first place. The American Academy of Ophthalmology identifies several common culprits: leaving eye makeup on overnight, using eyelash curlers (heated or not), and applying and removing lash extensions. The glue used for extensions can trigger allergic reactions, and pulling extensions off can take your natural lashes with them, damaging the follicle in the process.
Removing mascara roughly is another major source of mechanical lash loss. Waterproof formulas require more friction to remove, which tugs lashes out during the resting phase when they’re already loosely anchored. If you wear waterproof mascara regularly, use an oil-based remover and press a soaked cotton pad against your closed lid for 15 to 20 seconds before gently wiping downward. Rubbing back and forth is the fastest way to shed lashes you didn’t need to lose.
Nutrition and Lash Health
Biotin supplements are widely marketed for hair growth, but the evidence is thin. Biotin deficiency does cause hair loss, including lash loss, but true deficiency is rare in people eating a varied diet. A literature review found no published studies showing biotin supplementation helps hair growth in people who aren’t deficient. The same pattern holds for zinc: supplementing corrected hair loss in a child with zinc deficiency, but giving zinc to a group of 15 adults with hair loss and low zinc levels didn’t produce significant regrowth.
The practical takeaway: if your lashes have thinned noticeably and you also have brittle nails, fatigue, or skin changes, a nutrient deficiency might be involved and is worth checking with bloodwork. Otherwise, adding supplements on top of an adequate diet is unlikely to change your lash thickness.
Professional Cosmetic Options
If you want the look of thicker lashes without waiting months for a serum to work, professional lash lifts and tints offer a faster route. A lash lift curls your natural lashes upward using a chemical solution, making them more visible. A tint darkens them so they appear denser. Lifts typically last six to eight weeks, while tints fade in three to four weeks.
These aren’t risk-free. The chemicals used in lash lifts (ammonium thioglycolate, thioglycolic acid, or cysteamine hydrochloride) can cause burns or allergic reactions if they contact the eye surface or surrounding skin. Most lash dyes are formulated for scalp hair, not the delicate tissue around your eyes, and some contain compounds that trigger severe allergic responses, particularly in people with previous dye sensitivities. If you go this route, choose an experienced technician and request a patch test beforehand.
Putting It All Together
The fastest, most reliable path to thicker lashes is a prescription bimatoprost serum, with visible results by about six weeks and full results by three to four months. OTC peptide serums offer a gentler alternative with more modest improvements, showing measurable thickness gains within 30 days. Castor oil adds shine but not growth. And the simplest thing you can do starting tonight is handle your lashes more gently: remove makeup with care, skip the curler when you can, and give extensions a break. Lash follicles are small, but they’re surprisingly resilient when you stop working against them.