Lash Growth Serums That Actually Work: What the Science Says About Peptides, Prostaglandins, and Natural Oils

February 16, 2026|Bianca Virtudazo

Healthy lash habits demonstrated by a model applying Pro Lash adhesive carefully while using a compact mirror outdoors.

The lash serum market is projected to reach $1.3 billion by 2031, up from $752 million in 2020, driven by viral before-and-after photos, influencer endorsements, and the promise of longer, thicker lashes with minimal effort. Scroll any beauty forum, and you will see dramatic timelines and confident testimonials that make results feel inevitable. In reality, lash growth is gradual and highly individual. Formulas vary, consistency matters, and lighting, mascara, lash lifts, and filters can exaggerate progress. The truth is more nuanced.

How Eyelashes Actually Grow: The Biology You Need to Understand First

Before evaluating any serum, it helps to understand what it's trying to influence. Eyelashes grow in a cyclical pattern with three distinct phases, and the entire cycle lasts roughly five to twelve months:

The Anagen phase is when the lash is connected to its blood supply through the dermal papilla, receiving the nutrients it needs to lengthen. Lashes grow at roughly 0.12 to 0.14 mm per day during anagen, which lasts four to ten weeks. At any given time, only about 40% of your upper lashes and 15% of your lower lashes are in this phase. The majority of your lashes are either transitioning or resting at any moment.
The catagen phase follows, lasting two to three weeks. The follicle shrinks, detaches from its blood supply, and the lash stops growing.
Then comes the telogen phase, a resting period of roughly 100 days before the lash naturally sheds and the cycle restarts.

This is the core mechanism every lash serum targets: extending the anagen phase so lashes grow longer before they transition, or stimulating resting follicles to re-enter the growth phase sooner. Understanding this biology is essential because it explains both why serums take 8–16 weeks to show results and why they must be used consistently.

Volume lash set displayed in Pro Lash starter kit with lashes, adhesive, remover, and applicator tools arranged neatly.

Prostaglandin Analogs

If you want to cut straight to the ingredient with the strongest clinical backing, it's bimatoprost — a synthetic prostamide analog originally developed to treat glaucoma. Eyelash growth was discovered as a side effect in glaucoma patients in the late 1990s, which eventually led to its development as a dedicated lash treatment.

Multiple randomized controlled trials have replicated these findings. A separate study evaluating bimatoprost for chemotherapy-induced eyelash loss confirmed its efficacy in that population as well. Bimatoprost remains the only FDA-approved treatment for eyelash hypotrichosis, marketed as Latisse. No other lash serum ingredient has this level of regulatory validation.

The Prostaglandin Analog Gray Zone

Here’s where it gets complicated. Many over-the-counter lash serums contain isopropyl cloprostenate, a synthetic prostaglandin analog that is structurally similar to bimatoprost. Because these products are sold as cosmetics, they can sit in a gray zone where marketing promises can sound drug-like, while the evidence base and oversight may not match what consumers assume.

Clinical recommendations for isopropyl cloprostenate are difficult in the absence of formal research on its efficacy and with limited safety data. In other words, you may see dramatic claims online, but there is not enough high-quality human research to clearly quantify results or fully map risks, especially with long-term use near sensitive eye tissue. If you have sensitive eyes, consider avoiding it or asking an ophthalmologist before using.

Peptides

The three most common peptide ingredients in modern lash serums are myristoyl pentapeptide 17, biotinoyl tripeptide 1, and myristoyl pentapeptide 16. Together, they function as the workhorses of the prostaglandin-free serum category, meaning they are often used in formulas that avoid prostaglandin analogs while still promising visible improvement. These peptides are short chains of amino acids, and in skin and hair care, they are widely used as signaling molecules. The basic idea is not that peptides “create” new lashes overnight, but that they may help optimize the conditions that support healthier-looking lashes over time.

In lash serums, the proposed mechanism is fairly straightforward. Peptides like myristoyl pentapeptide 17 are often described as supporting keratin-related activity. Keratin is the structural protein that makes up the lash fiber, so increasing keratin production or improving keratin organization could, in theory, lead to lashes that look denser, stronger, and less prone to snapping. Myristoyl pentapeptide 16 is frequently included for similar reasons, since it is positioned as another keratin supporting signal. If a serum helps lashes break less, you may notice a gradual improvement in visible length simply because more of each lash stays intact through cleansing, rubbing, and mascara removal.

Biotinoyl tripeptide 1 is usually marketed a little differently. Rather than focusing only on the lash shaft, it is often framed as supporting the follicle environment and lash anchorage. In practical terms, anchorage refers to how well the lash remains secured throughout its natural growth cycle. If an ingredient helps reduce premature shedding, the lash line may appear fuller over time because fewer lashes drop out earlier than expected. That is the appealing promise of this peptide category: less fallout, better retention, and healthier structure rather than a dramatic growth spurt. It is also why consistent daily use is emphasized, since any effect would likely show up gradually across multiple weeks.

Where things get complicated is the evidence. The ingredient manufacturer Symrise, which developed several of these peptides, has published clinical data suggesting that myristoyl pentapeptide 17 can increase the appearance of lash length, including claims around a 25 percent increase under specific study conditions. They also report that formulas combining peptides with glycosaminoglycans improved eyelash structure by week 12, with earlier signs of improvement by about week 4. Those results are encouraging, but they are still manufacturer-generated findings, often tied to a specific ingredient blend, concentration, and testing method. In the real world, outcomes can vary based on formulation quality, how close the product is applied to the lash line, user consistency, baseline lash health, and whether “improvement” is measured as true growth or simply better retention and reduced breakage.

Natural volume lashes featured in close-up of a model brushing extensions with a spoolie for soft, full definition.

What This Means in Practice

Peptide-based serums are almost certainly safer than prostaglandin analogs. They don't carry the risk of iris darkening, periorbital fat loss, or the other serious side effects associated with prostaglandins. Individual variation in genetics, baseline lash health, and the specific formulation all play roles that current research hasn't untangled. If you choose a peptide-based serum, look for products that list specific peptides, myristoyl pentapeptide-17, biotinoyl tripeptide-1, or acetyl tetrapeptide-3, high on the ingredient list, suggesting meaningful concentrations rather than trace amounts added for label appeal.

Castor Oil

Castor oil is the darling of the natural beauty world when it comes to lash growth. It is inexpensive, widely available, and it fits perfectly into the “one simple hack” format that spreads fast online. Scroll through social media, and you will find countless routines and before-and-after photos suggesting that brushing castor oil along the lash line can transform sparse lashes into thick, dramatic fringe. But most of that content blurs an important distinction: making lashes look better is not the same as making lashes grow more. Eyelashes grow on a slow cycle, and true changes in length or density typically require time, consistent conditions, and strong clinical evidence. Castor oil’s popularity often outpaces what we can confidently claim it does at the follicle level.

What castor oil can do more reliably is act like a cosmetic conditioner. Because it is thick and highly occlusive, it can coat the lash shaft, reducing friction from cleansing, rubbing, and mascara removal. When lashes break less, they can appear longer over time simply because more of each lash stays intact. That coating can also create a temporary “fuller” look by smoothing and slightly plumping the appearance of individual lashes, especially when they are brushed into place. Where the evidence is more supportive is on comfort and lid health in certain contexts. For example, one small clinical report found that using 100% cold pressed castor oil on the eyelids twice daily for four weeks was associated with significant improvement in blepharitis symptoms, which matters because irritated lids can trigger rubbing and worsen lash loss through mechanical damage.

Still, castor oil is not risk-free around the eyes. Its viscous texture can migrate, blur vision, or irritate sensitive tissue, and “natural” does not rule out allergy. If someone chooses to use it, the safest approach is minimal product, careful placement away from the waterline, and stopping immediately if there is stinging, redness, swelling, or persistent irritation.

Other Natural Oils

Natural ingredients with plausible mechanisms for lash support include pumpkin seed oil, ginseng, and coffee extract. In theory, these may improve the look and feel of lashes through pathways tied to collagen support, keratin-related processes, and antioxidant protection.

Pumpkin seed oil is often discussed for its fatty acid profile and plant sterols, which may help condition hair fibers and support the skin barrier around the lash line. When lashes are better conditioned, they can appear glossier, feel softer, and break less easily, which can translate into the impression of fuller lashes over time, even if the number of lashes does not change.
Ginseng is frequently described as a stimulating botanical in hair care because it contains ginsenosides, compounds studied for potential effects on cellular signaling. Applied near the lash line, the theoretical benefit is improved support of the follicle environment.
Coffee extract, often included for its caffeine content and polyphenols, is typically positioned as an antioxidant ingredient. If a formula reduces lash brittleness or improves flexibility, you may notice less shedding from breakage and better lash presence when you curl or apply mascara.

The key point, though, is that plausibility is not proof. Like castor oil, these ingredients still lack strong human evidence from rigorous trials specifically measuring eyelash length, density, and thickness over time. Used carefully, natural oils are generally low risk, but the eye area is sensitive. For those who want a simpler, non-serum option, eyelash extensions like Pro Lash can be a practical alternative, offering a lash-focused option that prioritizes appearance and routine-friendliness without relying on traditional lash-serum claims.

Caring for lash extensions shown with Pro Lash adhesive displayed on stone blocks, highlighting proper storage and product care.

The right choice depends on your priorities. If maximum efficacy matters most and you're willing to accept the risk profile, a conversation with a dermatologist or ophthalmologist about prescription bimatoprost is the evidence-backed path. If you want a lower-risk option and can accept that results may be modest or absent, a well-formulated peptide serum is a reasonable middle ground. And if your lashes are primarily suffering from dryness and breakage rather than slow growth, conditioning with a natural oil may be all you need. Whatever you choose, the single most important thing you can do is read the ingredient list, not the marketing copy.