We present the effect of electric field, temperature, humidity, type of elastomer material, and encapsulation on the lifetime of silicone-based dielectric elastomer actuators (DEAs) under DC electric fields. DEAs are promising soft actuators, but little has been reported on their reliability under static electric fields. We report that humidity and electric field are the dominant accelerating factors for device failure, and that a thin encapsulation layer can increase lifetime by more than an order of magnitude with negligible reduction in actuation strain. Our samples are expanding circle, single layer, prestretched films with 5 mm diameter compliant electrodes, operated at electric fields from 80 V mu m(-1) to 110 V mu m(-1), with actuation strains from 2% to 6%. We compare four different silicone elastomers, finding highest lifetime with Momentive Electro 242-1, five times higher than Elastosil 2030. Typical mean time to failure (MTTF) for Elastosil 2030 based DEAs at 100 V mu m(-1), 85 degrees C and 85% RH are 1.6 h, but this value increases to over 200 h at 20% RH. At 85 degrees C and 85% RH, the MTTF decreases by a factor of 62 when increasing the electric field from 80 V mu m(-1) (2.1% actuation strain) to 100 V mu m(-1) (4.6% actuation strain). Adding a thin, soft silicone encapsulation layer is an effective yet simple strategy to increase DEA lifetime, increasing the MTTF by factors from 2.2 to 75 under humid conditions. Extrapolating from our data, we predict that DC lifetimes above 1000 h can be achieved at fields below 70 V mu m(-1) (i.e. approximate to 1.5% strain) for Elastosil 2030/20 DEAs, and below 85 V mu m(-1) (i.e. approximate to 2.5% strain) for encapsulated DEAs at 85 degrees C-85% RH.