The derma roller, a handheld microneedling device made with hundreds of tiny needles used to poke holes into the face to make skin look younger, is estimated to be 2018’s hottest at-home beauty product, according to Pinterest. But experts say it’s ineffective, and even dangerous in the wrong hands.

Dermatologists are highly against using the tools at home because they say the needles aren’t big enough to penetrate the proper holes into skin, so you’re essentially damaging your face for no reason. And without proper sterilization, derma rollers can harbor harmful bacteria causing infections, breakouts and can trigger skin conditions such as rosacea, which causes redness and bumps on the face; eczema, itchy inflammation spots; and melasma, brown patches on the skin.