A Christmas tree rash is a skin irritation that occurs after contact with a Christmas tree. The rash may be caused by the sap from the tree or from mold spores that can accumulate on the tree's needles. Symptoms of the Christmas tree rash can include itching, redness, and even blisters in some cases. The rash typically resolves itself within a few days, but if you experience any severe symptoms or if the rash is not improving, it is best to consult a doctor.