Some oils can be harmful, especially for cats. Avoid:
Tea Tree (Melaleuca), Citrus, Wintergreen, Birch
Synthetic or low-quality oils
Oils to avoid if your pet is epileptic or has seizures:
Rosemary, Fennel, Sage, Camphor, Eucalyptus, Basil, Wintergreen and all the blends that contain these oils
Oils to avoid if your pet has a clotting or bleeding disorder or are taking an anticoagulant:
Wintergreen, Blue tansy, Cassia, Cinnamon, Clove, Fennel, Marjoram, Oregano, Patchouli and Thyme
Oils to avoid if your pet is on anti-diabetic drugs without careful blood glucose monitoring:
Cassia, Cinnamon, Dill, Fennel, Lemongrass, Marjoram, Melissa, Myrrh and Oregano
Photosensitizing oils may cause burning in pink skinned animals if used topically within 24hrs of UV exposure:
Bergamot, Cumin, Grapefruit, Lemon, Lime, Tangerine and Orange
A NOTE ON FISH : Clove sedates fish, so use caution with or around your aquariums. However, essential oils can be helpful for fish as well. Oils that can be used safely around fish : Copaiba, Frankincense, Citrus oils, Peppermint, Lavender, Roman Chamomile and many others