Eucalyptus oil and compounds in eucalyptus have proven to be harmful to dogs. If a dog happens to ingest eucalyptus leaves, bark, or oil, it may cause vomiting, diarrhea, drooling, weakness, or confusion in the dog. Even the smell of eucalyptus oil may irritate a dog’s respiratory system. Since dogs are sensitive to a wide range of toxins found in plants, it would be advisable to avoid exposing them to eucalyptus plants or oil. If a dog happens to show unusual symptoms after exposure to eucalyptus oil or plants, it would be advisable to contact a veterinarian.