If a patient has a low fever every afternoon, it is usually due to the following reasons: First, the most common factor is infectious. A low fever usually occurs when the body is infected with bacteria, viruses or other atypical pathogens and pathogenic microorganisms. And if infected by tuberculin, low fever occurs every afternoon. Secondly, endocrine disorders, such as hyperthyroidism and hyperadrenocorticism, may occur in the afternoon every day. Third, when the endocrine environment of women is dysfunctional, low fever may occur every afternoon, for example, during menopause or puberty. Fourth, some rare diseases may cause low fever every afternoon due to the destruction of the immune system, such as serious tumors, blood disorders, and AIDS.