Laser hair removal technology has been growing for decades and—like stubborn stubble—isn’t going anywhere anytime soon. You hear about it every time you surf daily deals, and your local spa may offer it. But things can get hairy if you don’t have the full 411. We talked to leading skincare experts and laser hair removal spas to bring you five things you need to know before you get zapped.

1. The wrong laser can do damage.

Choosing the right laser for your hair color/skin color combo can be the difference between hairless bliss and a trip to the ER.“Hair removal lasers are basically attracted to dark pigment in our hair follicle, which absorb different energies,” says dermatologist Anne Chapas, M.D., Medical Director for Union Square Laser Dermatology in Manhattan. The energies are different wavelengths of light, each suited for a particular unique skin and hair combination.

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 “For a laser hair treatment to be safe and effective, the right laser must be used for that individual’s skin and hair type,” says Dr. Mitchell Chasin, Medical Director of Reflections Center for Skin & Body in New Jersey. “Using the wrong laser can create unsightly lightening or darkening of the skin in the treatment area and sometimes even burns. Or the treatment simply might not work at all,“ he adds.

The general consensus from leading dermatologists: You can get in big trouble if you sign up for the first hair removal offer that hits your inbox. Follow our goof-proof guide to make sure you’re getting the right laser for you:

  • Alexandrite laser– This laser, a 755-nanometer wavelength of light coming from an Alexandrite crystal, is the gold standard for fair-skinned women with dark hair. “You want the laser energy to be absorbed by your hair follicle and not by the surrounding skin, which also has pigment in it. So it’s ideal for someone very fair with dark hair,” says Jennifer, a technician at Pulse Laser and Skincare Center.
  • Diode laser– This computer-generated, 810-nanometer wavelength treats lighter skintones and some light olive skintones.
  • YAG laser– The longer 1,064 wavelength from a synthetic crystalline material is less readily taken up by pigment, which makes these lasers effective for darker skintones or tanned skin.

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“All the melanin in Asian, Hispanic, African American and Indian-type skin ends up attracting the Alexandrite laser, so none of the energy makes it to the hair,” says Dr. Chapas. “The YAG laser goes deeper, becoming less absorbed by pigment in the skin,” she adds.These days, the newest cutting-edge devices can combine lasers in one machine. “What’s nice about the GentleMax Pro device is that it has an Alexandrite laser and the long pulse YAG laser. So if someone comes in and they might be on the fence, I can say, ‘Okay, well this time we’re going to do the Alexandrite rather than the YAG,’” says Dr. Chapas.Bottom line? Dial up the derm office or spa ahead of time to see what lasers they offer.

2. Your hair will keep coming back until four to eight (yes, eight) sessions later.

Why, oh, why does it take so many treatments to work? Depending on the person and where on your body you’re having the hair removed, it may take anywhere from three to eight sessions (or more!), though usually something in between. The waiting is annoying, but there’s actually a solid scientific reason behind it. There are three stages of hair growth—and the only stage when a hair can actually get killed is when it’s actively growing. “If the roots of the hair are growing and connected to a blood supply, the heat from the laser kills the blood supply and it can’t form another hair,” says Jennifer of Pulse.

“The hair won’t get killed in the other two stages,” she adds. “Those are the hairs that will come back, which is why it often takes six sessions or more. You’re just waiting for that hair to cycle through.”In the meantime, you can follow protocol to make sure each session counts. “We try to do the same follow-up care: Keep out of the sun, shave in between treatments, and don’t wax or pluck the hairs out because your next treatment won’t be as effective,” Dr. Chapas says.

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That said, some lasers do require a little bit of stubble. With others, its relatively important to have a decently good shave before going in. Again, call your spa and ask what level of hair is specifically required for the laser you’re using.

3. It’s not as scary as it sounds.The truth? Lasering isn’t much worse than waxing, if at all. For pain control, you can apply a prescription strength cream with 4-5 percent lidocaine, like Emla, an hour prior. Ibuprofen helps more with inflammation than pain.

As for the rumors that some lasers are harsher than others, Dr. Chapas says that they basically all feel quite similar: like a snap or a rubber band across the skin (the YAG can hurt a bit more, since it’s used on dark skin, where there’s a lot of pigment around to soak up energy). The price is where it really hurts! One session costs about five times as much as waxing. But if you wax on the regular, laser hair removal is cheaper in long run.

4. There’s a debate between dermatologists and laser hair removal spas. The laser hair removal spa side: If you want to go to your dermatologist, make sure they do the treatment themselves, Jennifer of Pulse advises. Derm offices may not have the range of lasers available to meet your needs—plus, their machines may be rented and slightly out of date, she notes.

The dermatologist side: “I’ve seen a lot of complications with non-physicians, particularly with laser hair removal,” says Dr. Chapas. “You’re better off doing it with a dermatologist who specializes with problems of the skin. [If you don’t] you’re putting yourself at risk,” Dr. Chapas says.

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Bottom line: States have different licensing requirements for laser hair removal. If you’re not seeing a doctor, check if they’re licensed to practice skincare, and have taken specific classes on laser technology.

5. Read the fine print and give background information.

While every place preps differently, they all need to gather essential information to make sure you aren’t doing anything that can interfere with the treatment.

“The lasers aren’t intelligent enough to know your skin color versus your hair color,” says Jennifer. “That’s why they ask you stay out of the sun for four weeks for the Alexandrite laser, and two weeks for the YAG.”Some oral antibiotics can make your skin light-sensitive, so make sure you haven’t taken any in the last two weeks, Jennifer adds. A good rule of thumb: If no one is asking you for this kind of background information, pack up and leave before they fire that laser up!