Yes, dogs can be allergic to Christmas trees. Many dogs have sensitive respiratory systems and can be affected by the strong odor of Christmas trees, which can trigger sneezing, coughing, and other respiratory symptoms. Additionally, some dogs may be allergic to the sap or pollen produced by the Christmas tree, which can cause skin irritation and other allergic reactions. If you are concerned that your dog may be allergic to your Christmas tree, it's best to consult with your veterinarian for advice.