If you have had a cold for more than a month, it may be caused by autoimmune deficiency, rhinitis, or other diseases with symptoms similar to those of a cold. 1. Autoimmune deficiency: autoimmune deficiency can cause colds and flu, and the symptoms will not be relieved for a long time, thus the cold has been bad for more than a month. 2. Rhinitis: Inflammation of the nasal cavity caused by viruses, bacteria, allergens and other causes. Itchy nose, nasal congestion, sneezing and runny nose are the main symptoms. 3. Other diseases: If the symptoms are not relieved for a long time when you have a cold, you need to be alert to the possibility of other diseases, such as nasopharyngeal cancer. When the cold has been bad for more than a month, it can also be seen in other reasons, patients need to choose regular medical institutions, and follow the doctor’s instructions for treatment as soon as possible.