If you've shopped for a lash growth serum, you've probably noticed that the best-known formulas quietly rely on the same class of ingredient: a prostaglandin analog. These ingredients can produce visible results, but they're also the reason a lot of people end up searching for their side effects. Here's a clear, honest look at what prostaglandins do, what can go wrong, and what to look for if you have sensitive eyes.
What are prostaglandins in lash serums?
Prostaglandin analogs (ingredients with names like isopropyl cloprostenate, bimatoprost, or similar “-prost” compounds) were first used in medicine to treat glaucoma. Doctors noticed a side effect: patients' eyelashes grew longer and darker. That side effect became the basis for prescription and over-the-counter lash serums. They work by extending the growth phase of the lash cycle, which is effective, but comes with trade-offs.
Common side effects to know about
Reactions vary from person to person, and many users have no issues. But the side effects reported with prostaglandin-based serums are well documented and worth understanding before you commit to daily use around your eyes:
- Eye and eyelid irritation — redness, itching, stinging, or burning, especially early on.
- Eyelid skin darkening (hyperpigmentation) — the skin along the lash line can deepen in color; it often fades after stopping, but not always for everyone.
- Iris color change — with some prostaglandins, a permanent darkening of the colored part of the eye has been reported. This is the side effect people find most alarming.
- Dryness, or a sunken/hollow look around the eye — sometimes called orbital fat loss, reported with longer-term use of certain analogs.
The important context: cosmetic lash serums aren't held to the same dosing and monitoring standards as a prescription medicine. That's why so many shoppers who've had a reaction, or who simply don't want the risk, start looking for a prostaglandin-free option.
How to tell if your serum contains a prostaglandin
Check the ingredient list (the INCI list) for anything ending in “-prost” or names like isopropyl cloprostenate, isopropanol phenyl-hydroxy-pentene dihydro-trimethyl-cyclopentyl heptenate, or dechloro dihydroxy difluoro ethylcloprostenolamide. If a brand won't clearly tell you whether it's prostaglandin-free, treat that as your answer.
The prostaglandin-free alternative
A newer generation of serums skips prostaglandins entirely and uses peptides and botanicals to support the look of longer, fuller, healthier lashes, a cleaner profile for sensitive eyes. That's the approach we take at Boru: prostaglandin-free by design, peptide-powered, and formulated professional-first. You can read more about how prostaglandin-free serums work and the peptides that matter in our other guides, or learn about our story.
This article is for general education and isn't medical advice. If you're experiencing a reaction to any product, stop use and talk to a doctor or eye-care professional.