Eyelash extensions are semipermanent lashes that are hand-glued on top of your natural lashes, says Andra Marin, artistic director and expert lash stylist at Courtney Akai Lash Boutique in NYC. Unlike strip lashes, lash extensions are glued on individually to your natural hairs, so they’re super customizable and actually look real.

How long do eyelash extensions last?

If you actually take care of them (more on that later), eyelash extensions can last for six to eight weeks until they naturally fall out like your lashes usually do. Once they start falling out, though, you can go back and have your lash stylist fill in the missing pieces. So, technically, you can make your extensions last indefinitely.

Do eyelash extensions ruin your eyelashes?

Not really—there isn’t a ton of evidence that shows whether eyelash extensions actually affect your natural lash length or health long-term. There is, however, a teeny-tiny risk of developing traction alopecia, says Zaina Al-Mohtaseb, MD, assistant professor of ophthalmology at Baylor College of Medicine in Houston, which is where your natural lashes can fall out as a result of the constant weight of repeated eyelash extensions. But don’t stress—this isn’t common.

“Usually, it takes years of bad application and improper care for long-term lash damage to happen as a result,” says Marin. So please, only go to legit, well-reviewed salons (no matter how good that Groupon deal is). Make sure your technician follows all the sanitation and disinfection protocols, and don’t feel awkward asking your technician to confirm that all of these precautions are being taken. And remember: Listen to your gut. If you’re getting a bad vibe from a salon, reschedule.

What’s bad about eyelash extensions?

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Eyelash extensions aren’t dangerous or “bad” as long as your technician is following the correct methods and using the proper materials. Before you head to your appointment, ask the salon about the ingredients in the lash glue they use. If they can’t answer your question, cancel the appointment (you don’t want inexperienced people sticking things to your eyelids), and if they say the glue contains formaldehyde (a known eye irritant that can cause redness, irritation, and itchy, swollen eyelids), def cancel the appointment. It may cost you a little more, but it’s best to choose a salon that uses “glues made with butyl cyanoacrylate and octyl cyanoacrylate instead of formaldehyde—they’re less toxic to the eye area,” says Dr. Al-Mohtaseb.

Also important to note? The difference between a certification and a license. Phillips points out that just because someone has a bunch of certifications, that doesn’t mean they’re licensed by the state and health department. Some states require lash techs to be licensed, so make sure that the person you’re seeing checks all the required boxes.

How much does a full set of eyelash extensions cost?

It depends on where you live, but in New York City, a basic set (typically 70 to 80 lashes per eye) can range anywhere from $100 to $400 plus tip, which is usually another 20 percent. And because eyelashes grow and eventually fall out, you have to go back every few weeks for fill-ins, which can cost anywhere from $50 to $165, depending on how many new lashes you need.

PSA: The longer you go between fill-ins, the more lashes you’ll need to replace and the more it will cost you—and if you wait too long, your technician might just want to give you a brand-new set of extensions rather than a fill-in, which obviously won’t be cheap.