Lash serums promise longer, fuller lashes in a few weeks. They are all over your feed and probably sitting in your cart. But before you start applying them near your eyes, you should know that some ingredients in lash serums can do more harm than good.

To begin with, they contain prostaglandin analogs, or PGAs, the same stuff used in glaucoma meds. These compounds can cause burning, stinging, and dryness. If the serum gets into your eyes, it may trigger redness that doesn’t go away quickly.

For people with sensitive eyes, this can be a nightmare. Even if the formula stays on the lash line, irritation can still happen. PGAs are powerful, and your eyes are delicate. Not a great match if you are hoping for comfort and results.

Skin Darkening

PGAs do more than grow lashes. They can also darken the skin around your eyes. Some people notice a shadowy ring or darker lash line that sticks around. In rare cases, especially in people with light eyes, these serums can even change eye color permanently.

This is more than a cosmetic side effect. Once the pigment shifts, there’s no going back. What starts as a beauty routine could turn into a regret you see in the mirror every day.

Hollow Eyes and Sunken Lids

Some lash serums are linked to orbital fat loss. That means the soft tissue around your eyes can shrink, leading to a hollow, aged look. Dr. Umbareen Mahmood, a plastic surgeon, experienced this herself and had to get corrective surgery.

It doesn't happen to everyone, but when it does, it’s dramatic. The irony? A product meant to make your eyes look better can actually age them fast.

Allergic Reactions and Bacterial Buildup

Swelling, itching, and styes are also on the list of possible side effects. Bacterial buildup is common if you don't clean the applicator properly or if the serum clings to your lashes overnight.

Luca / Unsplash / If you wear contacts, you are at even higher risk. Residue from the serum can get trapped against your eye, causing infections or cloudiness.

It is uncomfortable and can mess with your vision.

Drooping Eyelids and Weak Muscles

Rare but serious, some users have reported muscle weakness in the eyelids. This can cause ptosis, or eyelid drooping. It can change your entire eye shape and, in some cases, require surgery to correct.

However, these aren’t mild side effects. They are medical issues caused by ingredients that aren’t always clearly explained on the label. Just because it is on a beauty shelf doesn’t mean it is harmless.

What Makes Some Lash Serums Risky?

Many over-the-counter lash serums use PGAs that are similar to prescription drugs like Latisse. One common ingredient is isopropyl cloprostenate. Sounds like a mouthful, but it mimics a drug without the FDA oversight.

That is risky. You are putting something next to your eyeball that hasn’t been fully tested. And most people don't know how to spot these ingredients. Look for names ending in "-prost." That is your red flag.

Hola / Pexels / Lash serums only work while you are using them. Stop applying, and the results fade fast.

In some cases, lashes fall out or look brittle after stopping. It is like a bad breakup for your eyes.

If you use them daily, it becomes a long-term habit, which means long-term exposure to all the risks we just discussed.

People with glaucoma, inflammation around the eyes, or contact lenses should think twice. PGAs can mess with eye pressure, interfere with meds, and make conditions worse.

Even if you are healthy, it is smart to talk to an eye doctor before starting a lash serum. Most people don’t think of lash serums as medical products, but when they contain drug-like ingredients, they act like them.