Not all diffusers are equal. You want to look for a diffuser that is ultrasonic, cold air diffusing, with an auto-shutoff and timer setting.
For best results, clean the diffuser occasionally buy putting 2 Tbsp of white vinegar in the tank and let it sit for at least 20 minutes. Clean with a soft tip cotton swab to remove build-up. Wipe the inside of the tank with a paper towel. Do not use chlorine. Run the diffuser for 10 to 15 minutes with water only to help clear the ultrasonic mechanism.
Only use 100% pure essential oils in your diffuser. Synthetic or fragrance oils can cause damage.
Do not scrap or scratch the ultrasonic mechanism in the water tank.
Turn the diffuser off before removing the cover.
Do not get water in the air outlet vent, it will damage the diffuser.