Unfortunately, yes, cats can be allergic to Christmas trees. The sap of pine trees can cause skin irritation and respiratory problems in some felines. Symptoms include sneezing, itching, coughing, and even vomiting. If you have a cat, it's best to choose an artificial tree or use a tree that has been treated to remove its sap. And make sure to keep any decorations or ornaments out of your cat's reach, as some can be toxic if ingested.