If you have a low fever every night, there are usually several factors as follows: 1. The most common factor is infectious. Bacterial infections, viral infections, fungal infections and atypical pathogens such as mycoplasma or chlamydia infections can occur when a low fever accompanied by peripheral discomfort occurs every night. Tuberculosis and AIDS can also present with recurrent low-grade fever. Non-infectious diseases, including diseases caused by immune deficiency or connective tissue diseases, rheumatic diseases, such as dermatomyositis and systemic lupus erythematosus, may also present with the above clinical symptoms and manifestations. 3. Anemia and tumors can also cause a low fever every night.