Safety guidelines for diffusion:

“Intermittent diffusion is much more effective, as well as being safer, than continuous diffusion. Intermittent means 30-60 minutes on, then 30-60 minutes off.

This is because our body, especially our nervous system, habituates after this length of time. With continuous diffusion, while benefits do not increase, there is evidence that the body becomes stressed in various ways.

However, very low levels of diffusion – so the essential oil is barely noticeable – are fine anywhere, for any length of time.”
~ Robert Tisserand