What is basal body temperature?

In clinical practice, basal body temperature refers to the body temperature under basal conditions, typically measured in the morning after waking up and before engaging in any activity. The normal range varies depending on the measurement site: axillary temperature ranges from 36.0℃ to 37.0℃, sublingual temperature from 36.3℃ to 37.2℃, and rectal temperature from 36.5℃ to 37.7℃. Basal body temperature is influenced by multiple factors such as circadian rhythm and indoor-outdoor temperature differences, typically being lower in the early morning and higher in the afternoon and evening. Additionally, measurement of basal body temperature is commonly used in clinical settings to assess febrile illnesses and to estimate women's menstrual cycles and ovulation times. If the body temperature is found to be abnormally high or low, diagnosis and treatment should be carried out in combination with the specific clinical context.