Carnations (Dianthus caryophyllus) are only mildly toxic and usually include gastrointestinal upset. Diarrhea, drooling, loss of appetite, and vomiting are indications that your cat may have chewed on carnations in the garden.
Carnations and other dianthus species contain toxic irritant triterpenoid saponins. This irritant makes them poisonous to cats and dogs as well as rabbits.
For this reason a cat can have stomach problems. Because cats eat grass and a variety of plants that aid in digestion – including carnations and their relatives, and often vomit afterward, it can be difficult to determine whether a few carnation petals is the cause of the stomach upset.
But a cat doesn’t have to eat carnations to suffer an adverse reaction: If your cat’s skin comes in contact with carnations, it can develop dermatitis, an inflamed skin rash.
Generally, if a cat vomits once or twice, that usually purifies her system of the irritant. If your cat has vomiting or diarrhea for a long period of time, take her to the vet; maybe she ate something more toxic than a carnations.
Conclusion: Carnations are not the most dangerous houseplant for your cat. In general, the symptoms are mild to moderate. Usually carnation poisoning is not fatal, just unpleasant.