If you have a fever every day at night there are usually several diseases as follows: 1. The most common factors are infectious factors, such as bacterial infections, viral infections, fungal infections, and atypical pathogens such as mycoplasma or chlamydia when the clinical symptoms of fever occur at night, for example, children often have fever at night due to mycoplasma infections, while the elderly and immunocompromised people often have fever at night due to fungal infections will be particularly significant. 2. Non-infectious factors can also cause fever at night, such as tuberculosis, rheumatism, rheumatoid diseases and other connective tissue diseases such as dermatomyositis and systemic lupus erythematosus, etc. 3. Common allergic reactions can also cause fever at night. 4. Diseases caused by immune deficiency can also cause fever at night, and common conditions such as hematologic diseases, tumors, and AIDS can cause fever at night.