Is peppermint essential oil safe for cats? What if they just breathe in a little bit from a diffuser? No. Peppermint oil contains compounds like menthol and pulegone, which cats cannot metabolize effectively due to their liver’s inability to produce certain enzymes. This can lead to a toxic buildup in their system, potentially causing serious health issues such as liver damage, respiratory distress, or even neurological problems. Cats are particularly sensitive to essential oils, and peppermint oil is no exception.