Lash serums are one of the few beauty products that have earned the title of “miracle worker.” Over time, regular slicks of the stuff can help to keep your lashes healthy and nourished, preventing them from breaking off and providing an ideal environment for growth. With enough use, many people have even sworn off lash extension appointments altogether. The only downside? There are some lash serum side effects to be aware of.

From lash serum orbital fat loss to changes in eye color to eye irritation from lash serums, doctors recommend proceeding with caution when introducing these products into your routine. Here’s everything you should know before making a purchase.

How do lash serums work?

According to Kami Parsa, MD, a Beverly Hills-based oculoplastic surgeon who specializes in reconstructive surgery of the eyes and surrounding tissues, “lash serums contain a combination of ingredients that are aimed at nourishing and promoting lash growth.” (Kind of like what conditioner does for your hair.) You draw the product along your lash line, and the result—of course—is thicker, fuller-looking lashes that will save you a trip to the extension bar.

However, studies have shown that there are some side effects of lash serums to be aware of, particularly due to one ingredient: prostaglandin analogues.

The issue with prostaglandins

You may have already come across prostaglandin analogs without realizing it, as it’s the active ingredient in some of the most well-known lash enhancement products. Bimatoprost is the active ingredient in Latisse, while latanoprost, another prostaglandin, is what’s used in RevitaLash. (Read up on our RevitaLash review here.)

But what are prostaglandins, exactly, and what harm can they potentially cause? Prostaglandin analogues, which are derived from fatty acids, are considered “first-line therapy” for glaucoma, helping to relieve pressure inside the eyes of patients. These patients noticed an unexpected side effect after using it: longer and thicker lashes, which is due to the hormone-like effect that prostaglandins have on the growth cycle of lashes. This discovery led to the development of lash serum products.

Although it may seem like there are no drawbacks to accidentally achieving luscious lashes, the risks of using lash serums primarily stem from prostaglandins. “Besides the usual irritation and redness which can be seen with any product, this category of serums can cause darkening of the skin they come into contact with and may permanently darken iris color,” says Dr. Parsa. “Long-term, they may cause the loss of fat around the eyes, which I have seen in several patients.”

While Dr. Parsa says not all lash serums contain prostaglandins, those without their growth hormone-like effects aren’t typically as effective. “The only group that works is the prostaglandin agonists, and they come with these risks,” he says. If you’re concerned about experiencing eye irritation from lash serums, orbital fat loss, or hyperpigmentation issues, there are alternative ingredients to be on the lookout for.

Other lash serum ingredients

As for the rest of the ingredients commonly found in lash serums, Dr. Parsa says “there is a lack of good scientific evidence that [they] actually work.” (At least as well as prostaglandin-based options.) But the ingredients do come with benefits. When scanning the ingredients list of lash serums, he says you’ll likely find the following:

• Peptides, which are “amino acid chains that can support hair growth and health”
• Biotin, a “B-vitamin known for its role in hair health”
• Panthenol or provitamin B5, which “helps moisturize and condition lashes”
• Amino acids and proteins, which “support hair structure and strength”
• Natural oils like castor oil and argan oil, which “nourish and moisturize lashes”
• Plant extracts and antioxidants, which “provide additional nutrients and protection”

While the scientific evidence may be lacking on how these ingredients directly benefit your lashes, so many people claim to notice a difference in growth after using them that the prostaglandin-free alternatives are worth a shot.

4 side effects of lash serums

While there are always lash serum risks to be aware of when using any prostaglandin-based product, Mona Gohara, MD, a New Haven-based board-certified dermatologist, is the first to admit she’s still a fan—so long as you practice eyelash serum safety when using them. Lash serums are generally safe, and if you do experience any side effects, they typically go away when you stop using the product.

So, who’s most at risk of experiencing side effects of lash serums? According to Dr. Parsa, anyone who uses lash serums that contain prostaglandins should be aware of the potential negatives of lash enhancement products. However, some people are more at risk than others. “Although it is a smaller percentage of people who experience side effects, there are side effects to lash serums,” says Heather Yoo, an aesthetic physician’s assistant at SkinSpirit in Manhattan Beach, California. “The people most at risk for side effects from lash serum are people who have glaucoma and are already using eye drops for the treatment of glaucoma due to the decrease of intraocular pressure.”

If you’re concerned, the only way to mitigate the risks of using lash serums is to avoid prostaglandin-based options altogether. Or, obtain doctor or dermatologist advice, along with a few eyelash serum safety tips, before trying anything new. “These risks can be mitigated by verifying with [your] doctor first,” says Yoo. “Patients should also undergo eye exams to ensure optimum ocular health and decrease risks.”

1. Hyperpigmentation around the eyelids

Darker skin around your eyes is one of the biggest risks of using lash serums (and one of the most common dermatologist warnings you’ll hear), says Ranella Hirsch, MD, a board-certified dermatologist in Boston. While typically rare, it does happen, so it’s important to pay close attention to your skin when starting a lash serum for the first time.

Even though this is one of the prime dermatologist warnings about using lash serums, Dr. Gohara still says hyperpigmentation isn’t something to be too concerned about—it’s just something to be on the lookout for. “I’m all about lash-enhancing serums right now—just be careful of the hyperpigmentation, because sometimes that can be not-so-easy to fade down,” she says. “So don’t blow it off, but just be sure to take stock of it and make sure it’s really not discoloring your skin that much.”

If you do notice hyperpigmentation, Dr. Hirsch says the best way to remedy the situation is to practice eyelash serum safety by discontinuing the serum altogether.

2. Orbital fat loss

Lash serum orbital fat loss is a concerning side effect that’s been seen in individuals after using lash enhancement products. “Studies confirm some patients have experienced orbital fat loss after using bimatoprost with prolonged usage,” says Yoo. Most of the current research involves patients being treated with bimatoprost for glaucoma; there’s very little research that specifically confirms orbital fat loss due to prostaglandin-based lash serums. However, Dr. Parsa has noticed the loss of fat around the eyes in several of his patients due to the long-term use of prostaglandin analogs, so it’s something to be aware of.

3. Red itchy eyes

Another potential issue to keep in mind is eye irritation from lash serums. If this happens to you, it’s time for some dermatologist advice: Lisa Donofrio, MD, an associate clinical professor of dermatology at Yale University, says you can try using a bland moisturizer, like the Cetaphil Moisturizing Lotion ($12) or an over-the-counter five percent hydrocortisone cream ($11), to remedy the situation. If that doesn’t work, Dr. Hirsch the irritation “much improves by stopping” the use of the serum.

4. Changes in eye color

This is the rarest on the list and the one you should be the least worried about, explains Dr. Donofrio. “When the clinical trials were done for Latisse, there were no cases of change of eye color,” she says. “When the company went to submit their data to the FDA, the FDA said that they needed to add more subjects to the study, which would have delayed the launch of the product, so they struck a bargain. They could include the adverse effect data from the glaucoma clinical trials, which used eye drops of the same stuff that’s in Latisse. That’s where the eye color change can happen, not really with topical application.” Only about one percent of people in trials for bimatoprost, the glaucoma eye drops, experienced eye color change.”

Lash serum alternatives to consider

If you want to avoid prostaglandin-based lash serums (and the lash serum risks associated with them), there are plenty of alternatives to consider that don’t come with doctor or dermatologist warnings. For those seeking longer, thicker eyelashes, lash care and safety should be a top priority—and these tips are a great place to start.

Choose a moisturizing serum or conditioner

There are lash serum options available that don’t contain prostaglandins. Instead, they focus on ingredients that keep your lashes healthy—and, in turn, may make them longer and fuller. “Just like you condition your hair, you need to condition your lashes,” Clementina Richardson, celebrity lash expert and founder of Envious Lashes, previously told Well+Good. That’s why she recommends using an eyelash conditioner, as it contains ingredients that moisturize and strengthen your lashes.

So do eyelashes grow back, even when they’re feeling especially sparse? The answer is yes—with a little TLC. Try VEGAMOUR GRO Lash Serum ($68) or The Ordinary Multi-Peptide Lash and Brow Serum ($15). You could also go with Maybelline Lash Sensational Serum ($14), one of the best drugstore lash serum options.

Choose the right mascara

Is thinning one of your lash health concerns? Look to your go-to mascara, because it could be preventing you from having the long, thick eyelashes of your dreams. First of all, skip anything waterproof—it’s dehydrating and hard to remove, which can wreak havoc on your lashes. Prioritize lash care and safety by choosing something moisturizing and easy to remove, like one of the best mascaras for thin lashes. Westman Atelier Eye Love You Volumizing Mascara ($58), for example, has ingredients that not only volumize and define lashes, but also conditions them to keep them healthy and strong.

Eat your way to longer lashes

Yep, that’s right—if you have any lash health concerns, you can eat your way to healthier, longer lashes. Tabitha Fredrichs, a trichologist and fine hair specialist, recommends eating biotin- and vitamin B-rich foods like egg yolk, spinach, oats, avocado, nuts, seeds, and lean proteins. Vincent De Marco, trichologist and co-owner of Vincent Hair Artistry, says collagen-producing foods and foods rich in vitamin C (like bone broth and citrus fruits) are great, too. “I highly recommend taking a vitamin C time-released supplement, either in pill form or in liquid form,” De Marco previously told Well+Good. “They can help with not only eyelash repair, but skin and hair as well.”

Try using castor oil

While there isn’t scientific research that supports castor oil promoting eyelash growth, there are enough people claiming that it works to give it a try. After doing a patch test of pure castor oil on your skin to make sure there aren’t any adverse reactions (lash care and safety comes first!), you can apply it to your lash line using a cotton swab. Simply leave it on overnight then rinse it off in the morning.

Frequently asked questions about lash serums

Do lash serums have side effects?

Yes, there are lash serum side effects to be aware of. The main lash serum risks come from using prostaglandin-based products. “Some of the side effects of using eyelash serum include eye redness, pain, irritation, itching, or dryness, skin pigmentation or iris pigmentation (the iris is part of the eye that presents its color), fat loss around the eyes, sunken eyes, loss of eyelashes, and intraocular pressure decrease,” says Yoo. If you notice anything off, discontinue the use of the eye serum and get some doctor or dermatologist advice.

Is lash serum FDA-approved?

Currently, the only lash serum that is FDA-approved is Latisse. Anyone who wishes to try it must get a prescription from their doctor. According to the American Academy of Ophthalmology, other over-the-counter options have yet to be tested for safety and effectiveness by the FDA, despite promising similar effects. With that being said, that doesn’t mean over-the-counter lash serums haven’t been tested. Most are ophthalmologically tested, which means a product has been approved by ophthalmologists as safe to use around the eye area.

What should you avoid in lash serums?

What should be avoided in lash serums is different for everyone. Because of how delicate the eye area is, anyone with sensitivities or concerns should always speak to a doctor about any lash health concerns before trying one. Generally speaking, though, most risks—like lash serum orbital fat loss and eye irritation from lash serums—are associated with prostaglandin-based products.