Carnations are mildly toxic to cats. Ingesting any part of the carnation plant—stem, leaves, or petals—can cause gastrointestinal upset such as vomiting and diarrhea. The sap of carnations can also cause skin irritation or dermatitis upon contact. While the toxicity is considered mild and not fatal, it is best to keep carnations away from cats to avoid discomfort and potential health issues.