If you have turned a lash serum box over lately, you have probably seen a long, chemistry-heavy word near the top of the ingredient list: myristoyl pentapeptide-17. It shows up in a lot of serums that skip prostaglandin analogs, and it is one of the most common reasons shoppers end up searching “what are peptides in lash serum?”
This guide explains what a peptide is, why lash serums use them, how they differ from the prostaglandin drugs found in some products, and how much real evidence exists. If you want the bigger picture first, start with our pillar guide, Prostaglandin-Free Lash Serum: What It Means and Why It Matters.
The short version: peptides are cosmetic conditioning ingredients, not drugs. They are a popular choice for people who want to avoid prostaglandins, and it helps to keep your expectations grounded in what the science can and cannot say.
Key takeaways
- Peptides are short chains of amino acids. Cosmetic formulators use them as conditioning ingredients in skin, hair and lash products.
- Myristoyl pentapeptide-17 is a five-amino-acid peptide attached to a fatty acid (myristic acid), which is meant to help it work with skin and the lash line.
- Peptides are not prostaglandin analogs. Bimatoprost (Latisse) is the only FDA-approved drug for growing lashes, and it carries known side effects such as lid darkening.
- Independent, controlled research on peptide lash serums is limited, so read marketing claims carefully and focus on how the product looks and feels on your lashes.
What is a peptide?
A peptide is a short chain of amino acids, the same building blocks that make up proteins. Proteins are long chains, often hundreds of amino acids. Peptides are short, usually anywhere from two to a few dozen. A “pentapeptide” has five amino acids, a “hexapeptide” has six, and so on.
Peptides occur naturally in skin, where many of them act as signaling molecules. A 2021 review in Current Protein and Peptide Science describes how cosmetic peptides are now made mostly by chemical synthesis, and how cheaper manufacturing has made them a common ingredient in skin care [1]. That review sorts cosmetic peptides into four broad groups [1]:
- Signal peptides, which are designed to send messages to skin cells.
- Carrier peptides, which help deliver trace elements such as copper.
- Neurotransmitter-affecting peptides, the “relaxing” peptides used in some anti-wrinkle creams.
- Enzyme-inhibiting peptides, which are designed to slow enzymes that break down skin proteins.
Most peptides marketed for lashes fall loosely into the signal peptide family. That said, a category label tells you what a peptide is designed to do in a lab setting, not what it will visibly do on your lashes.
What myristoyl pentapeptide-17 actually is
The name breaks down into three parts:
- Myristoyl: a myristic acid group, a fatty acid naturally found in foods like nutmeg and coconut oil.
- Pentapeptide: a chain of five amino acids.
- -17: a catalog number that tells it apart from other pentapeptides in the cosmetic ingredient naming system.
Attaching a fatty acid to a peptide is called lipidation. Formulators do it because plain peptides are water-loving and do not travel into the oily outer layer of skin very well. A 2017 review in Cosmetics explains that modifying synthetic peptides can improve how they penetrate, bind and stay stable, and gives the example of a palmitoyl (fatty acid) version of a peptide that moves into skin layers where the plain version does not [2]. The same review is candid that much of the peptide research is small, sometimes unpublished, and often done on finished formulas with several active ingredients, which makes it hard to know what any single peptide contributes [2].
You will often see myristoyl pentapeptide-17 paired with a close cousin, myristoyl hexapeptide-16 or myristoyl pentapeptide-16. Lash formulas tend to use them as a team, alongside moisturizing and soothing ingredients.
Peptides vs. prostaglandin analogs
This is the comparison that matters most for most shoppers. Lash serums fall into two broad camps: those with prostaglandin analogs and those without. A 2024 review in the Journal of Cosmetic Dermatology uses exactly this split [3].
Prostaglandin analogs are drug molecules. Bimatoprost, sold by prescription as Latisse, is FDA approved to treat hypotrichosis (inadequate lashes) “by increasing their growth including length, thickness and darkness,” according to its FDA label [4]. That same label lists warnings about increased brown iris pigmentation that is likely to be permanent, darkening of the eyelid skin, and hair growth where the solution touches skin [4]. Many over-the-counter serums use a related analog such as isopropyl cloprostenate, which the American Academy of Ophthalmology notes is not FDA approved [5]. Our guide to spotting prostaglandin analogs on a label walks through the names to look for.
Peptides are a different kind of ingredient entirely. They are used as cosmetic conditioners, and products built around them are sold as cosmetics. The 2024 review concluded that bimatoprost has the strongest evidence, that other prostaglandin ingredients need more safety study, and that non-prostaglandin ingredients show promise but lack formal evidence for eyelash use [3].
| Peptide lash serums | Prostaglandin analog serums | |
|---|---|---|
| What it is | Cosmetic conditioning ingredients (short amino acid chains) | Drug molecules related to glaucoma eye drops |
| Examples on a label | Myristoyl pentapeptide-17, myristoyl hexapeptide-16 | Bimatoprost, isopropyl cloprostenate |
| Regulatory status | Sold as cosmetics | Bimatoprost is a prescription drug (Latisse); other analogs in OTC serums are not FDA approved |
| Known side effects in labeling | No drug label; watch for irritation like any eye-area cosmetic | Iris darkening, eyelid skin darkening, redness, hair growth outside the treated area |
| Strength of evidence | Limited independent, controlled research | Bimatoprost: many controlled studies |
If you are deciding between the two approaches, our comparison of Latisse vs. over-the-counter lash serums covers the trade-offs in more detail, and our side effects guide explains the pigment changes and fat-loss concerns linked to prostaglandins.
Why “cosmetic” matters for the words on the box
In the United States, whether a product is a cosmetic or a drug depends on its intended use. The FDA defines cosmetics as products for “cleansing, beautifying, promoting attractiveness, or altering the appearance,” while drugs are intended to treat disease or “to affect the structure or any function of the body” [6]. The FDA specifically lists claims that a product will “restore hair growth” as the kind of claim that makes something a drug [6].
That is why a peptide-based cosmetic serum should talk about how lashes look and feel: longer-looking, fuller-looking, conditioned, glossy. If a non-prescription serum promises to grow, regrow or “activate” lashes, that is a red flag about its marketing, and it is worth checking the label for a prostaglandin analog.
What the evidence does and does not show
Here is an honest summary of where things stand:
- Peptides are widely used in cosmetics. They are a common ingredient across skin care [1].
- Much of the peptide research is limited. Studies are often small, sometimes unpublished, and frequently test a full formula rather than a single peptide [2].
- Formal, independent evidence is thin. The 2024 review described non-prostaglandin ingredients as promising but lacking formal evidence for eyelash use [3].
- Results are about appearance. Conditioning ingredients can help lashes look healthier, softer and more defined, especially when you also stop habits that break lashes.
None of that makes peptides a bad choice. It just means you should judge a peptide serum by how it looks and feels on you over time, and be skeptical of dramatic before-and-after promises.
What else is usually in a peptide lash serum
Peptides rarely work alone in a formula. Typical supporting ingredients include:
- Humectants and soothing botanicals such as aloe, which help keep the formula comfortable on the lash line.
- Antioxidants such as vitamin E (tocopherol).
- Proteins and protein fragments such as hydrolyzed soy protein, which coat and condition the lash surface.
- Plant extracts such as sage (Salvia officinalis) or baicalin.
- Preservatives, which keep a water-based product safe to use near the eye once opened.
If you have sensitive eyes or known allergies, the full ingredient list matters more than the headline peptide. See our guide to lash serum for sensitive eyes for how to patch test and introduce a new product.
How to get the most out of a peptide serum
- Apply to clean, dry lash lines. Remove makeup first so the serum touches the base of the lashes. Our application guide has a step-by-step routine.
- Be consistent. Conditioning products depend on regular use, and lashes cycle slowly. Our explainer on how long lash serum takes covers the lash cycle.
- Treat lashes gently. Rubbing, harsh removers and heated curlers undo a lot of good. Read more in our lash care guide.
- Keep it clean. Do not share eye products, and stop using any product that irritates your eyes.
When to see a doctor
Peptide serums are cosmetics, and they are not meant to address medical lash loss. Talk with a doctor or eye care professional if:
- Your lashes are falling out suddenly, in patches, or along with brow or scalp hair.
- Your eyelids are red, scaly, swollen, crusty or itchy.
- You have eye pain, changes in vision, light sensitivity or discharge.
- Irritation from any eye product does not settle after you stop using it.
Our pillar on thin or falling eyelashes covers common causes, and lash resources can help you find an eye doctor or dermatologist.
Want a prostaglandin-free serum built around peptides?
XXtraLash is a prostaglandin-free eyelash serum that conditions lashes with myristoyl pentapeptide-17, myristoyl pentapeptide-16 and four bioengineered sh-polypeptides for a longer-looking, fuller-looking lash line. Each 3 mL bottle comes with a precision brush for applying right along the lash line.
Frequently asked questions
What does myristoyl pentapeptide-17 do in a lash serum?
It is a cosmetic conditioning peptide: five amino acids attached to a fatty acid that helps it work with skin. Lash serums use it to condition lashes so they look longer and fuller. Independent, controlled research on what it does by itself is limited.
Is myristoyl pentapeptide-17 a prostaglandin?
No. It is a peptide, a short chain of amino acids. Prostaglandin analogs such as bimatoprost and isopropyl cloprostenate are different molecules related to glaucoma eye drops.
Are peptide lash serums safer than prostaglandin serums?
Peptide serums do not carry the prostaglandin-specific warnings found on the bimatoprost label, such as iris and eyelid darkening. Any eye-area cosmetic can still cause irritation or allergy, so patch test and stop if your eyes react.
Do peptides grow eyelashes?
Only FDA-approved drugs can make growth claims. The only FDA-approved drug for growing lashes is bimatoprost (Latisse). Peptide serums are cosmetics designed to help lashes look longer and fuller.
Can I use a peptide lash serum on my eyebrows?
Many people do, but follow the product’s directions. Our guide to using lash serum on eyebrows covers what to know.
Related reading
- Prostaglandin-Free Lash Serum: What It Means and Why It Matters
- Lash Serums Explained: Types, Ingredients and How to Choose
- How to Spot Prostaglandin Analogs on a Lash Serum Label
- How to Choose the Best Prostaglandin-Free Lash Serum
- Can You Use Lash Serum on Your Eyebrows?
Sources
- Signal Peptides: Promising Ingredients in Cosmetics. Current Protein and Peptide Science, 2021;22(10):716-728.
- Schagen SK. Topical Peptide Treatments with Effective Anti-Aging Results. Cosmetics, 2017;4(2):16.
- Baiyasi M, et al. Eyelash serums: A comprehensive review. Journal of Cosmetic Dermatology, 2024.
- LATISSE (bimatoprost ophthalmic solution) 0.03% prescribing information. U.S. Food and Drug Administration.
- What You Should Know About Eyelash Growth Serums. American Academy of Ophthalmology, 2019.
- Is It a Cosmetic, a Drug, or Both? (Or Is It Soap?). U.S. Food and Drug Administration.
