Off-gassing or “new mattress smell” is caused by VOCs (volatile organic compounds) that leach from the bed. In rare cases, off-gassing can cause headaches, nausea, dizziness, and shortness of breath. To reduce your exposure to VOCs, shop for a mattress that is certified by CertiPUR-US or Green Guard Gold. These third-party organizations test the mattress and ensure a low VOC rating.