From sore breasts to mood swings, PMS is no joke – but there is a symptom that can catch you completely surprised. “The basal core body temperature may change during the menstrual cycle, with a higher temperature occurring during the luteal phase of the menstrual cycle after ovulation,” Shannon Clark, MD, FACOG, a double-board certified ob-gyn and mother-fetal professor medicine in Texas, told POPSUGAR. That’s right- you can run a slight fever until your period without ever getting sick.

Dr. Clark explained that hormone fluctuations during your cycle can cause your basal body temperature to rise anywhere from 0.3 to 1.0 degrees Celsius. Translation? If you typically drive a cool 98.6 degrees Fahrenheit, your temperature can go up to 100.4. This is not a huge tip, but it is enough to give you “period flu” where you feel damp and hotter than usual. Rest assured: you probably do not actually have the flu! Your body just does its thing and prepares for the main event.

If fertilization occurs instead, the core body temperature remains elevated until the corpus luteum – a clump of cells that help produce progesterone during early pregnancy – is no longer functional, which is typically at the end of the first trimester, Drs added. . Clark. However, if an egg is not fertilized, your temperature drops back to normal levels after menstruation.

Again, it is normal to run low fever during your period. If it is accompanied by other menstrual symptoms such as cramps, consider taking an NSAID such as ibuprofen to ease the discomfort. If the fever persists or if you experience other symptoms of an infection, it is best to talk to your doctor.