Yes, wandering Jew plants (Tradescantia species) are mildly toxic to cats. The sap in the stems can cause irritation to a cat's digestive tract and may lead to dermatitis-like skin irritation, especially where the cat comes into contact with the plant, such as the belly, groin, and chin. Symptoms in cats may include scratching, skin irritation, diarrhea, and vomiting. While consumption of leaves may not usually cause toxic reactions, the sap can be irritating and cause discomfort to cats, so it's best to keep these plants out of their reach. Hanging baskets or placing the plants in areas inaccessible to cats are recommended precautions to protect both cats and the plant.
