Surface dielectric barrier discharge performance deteriorates in humid air, with permanent and/or reversible degradation of its components. Plasma operation in a humid environment is unavoidable when humid air or water-containing materials are treated. Experimental and numerical results indicate that an electrically conductive thin film of water is responsible for ohmic dissipation and inhibited plasma ignition at high relative humidity. An alternative hybrid surface-volume dielectric barrier discharge design provides more stable and uniform plasma operation in high-humidity atmospheres.