Why do them: “Doctor fish,” also known as garra rufa, love to eat dead human skin cells, which they suck off of the body, revealing fresh skin underneath. The fish have made a splash in Europe and Asia, where they’re used for pedicures and to treat the symptoms of psoriasis, and are now becoming trendy stateside.

The problems: Living creatures are hard to sanitize. At least three states—Washington, New Hampshire and Texas—have issued regulations against doctor fish, saying there’s no way to guarantee the fish are clean. Martin Grassberger, M.D., who’s researched garra rufa at the Medical University of Vienna, says there’s another concern. Some spas use a different species of fish called the chinchin, which feeds more aggressively than garra rufa. Chinchin can draw blood and spread disease, particularly in communal pools where blood-borne illnesses like hepatitis B can be passed by fish or through water to open wounds. If you try a fish spa, Grassberger says, make sure you get a private, sanitized basin of water and that the spa uses only garra rufa fish.

Why do it: Waxing yanks unwanted body hair out by the roots. It’s faster than tweezing and lasts longer than shaving.

The problem: First off, burns from hot wax can be severe and are more common than you might think, according to the medical journal Burns. Waxing also leaves your body vulnerable to infection. In fact, the FDA advises people with weakened immune systems to avoid waxing entirely. Anyone using wrinkle creams or acne treatments that contain retinol should also rethink waxing. Retinol can make skin so sensitive that there’s a risk of it peeling off along with the hair. But the biggest worry is topical skin-numbing cream, often used to make waxing and laser hair removal less painful. The FDA says drugs in the cream can end up in your blood. Use too much of it, or a cream that contains too high a concentration of the numbing ingredients, and the results can be life-threatening or even fatal. It’s best to avoid numbing cream altogether, but if you do use it, the FDA says to choose a cream they’ve approved as safe, to use as little of the cream with the lowest amount of active ingredient as you can. The FDA also recommends leaving the skin uncovered (don’t cover the treated area with plastic wrap or other dressing), and says to pick the correct cream with your doctor’s help—not that of your hair stylist or spa technician.