It pays to be careful, though. Essential oils can cause issues like burns if you don’t properly dilute them with a carrier oil such as jojoba, almond, coconut, or oliveThe safest way to use them is via a diffuser , says Oula. Your machine's instruction manual should indicate how many drops to add, but a safe ratio is 20 drops of oil to 4 oz. of water. Let the diffuser run for 30 to 60 minutes.