Short answer: Yes. Philodendrons are toxic to cats. Details

• Toxin: Most philodendrons contain insoluble calcium oxalate crystals. When a cat chews or ingests parts of the plant, these crystals can irritate the mouth, tongue, and throat, and may cause drooling, pawing at the mouth, vomiting, and difficulty swallowing. In some cases, airway irritation or swelling can occur.

• Affected parts: All parts of the plant (leaves, stems, and roots) can contain the crystals and pose a risk if ingested.

• Severity: Symptoms range from mild oral irritation to more significant GI upset; severe cases are possible but uncommon with small exposures. Prompt veterinary evaluation is advised if ingestion or exposure is suspected.

• Prevention: Keep philodendrons out of reach, use barriers or high shelves, and consider cat-safe alternatives (e.g., spider plants, Boston ferns, areca palms) if a cat tends to chew plants.

• What to do if exposure occurs: Rinse the cat’s mouth if you can do so safely, remove plant material from the mouth, monitor for symptoms, and contact a veterinarian for guidance. In more serious cases, professional care may include treatment to manage airway irritation, vomiting, or other symptoms.

If you’d like, I can summarize which common philodendron varieties are frequently kept as houseplants and confirm whether specific cultivars are considered more or less risky for cats.