Yes, real Christmas trees can be harmful to dogs. Pine needles are very sharp and can cause gastrointestinal distress if ingested. Also, the sap from the tree can cause skin irritation or respiratory issues. It is important to keep your dog away from the tree and not let them play with or chew on the branches. Additionally, if you have an artificial tree, be sure to check the materials it is made from as some may also be hazardous to pets.