No matter how long many of us have had them, it appears that we are still subjected to whiplash when they eventually appear each month (or whatever your specific cycle pattern is) and bring with them a slew of symptoms.

Whether it’s mood swings, excruciating cramps, skin breakouts, bloating, food cravings, lethargy, difficulty sleeping, body dysmorphia, a lack of sex desire, or any of the other innumerable bleeding-related side effects, periods can be extremely unpleasant at times.

Interestingly, many people who have periods report that the second day is the worst.

And this is not an old wives’ tale, as health scientists have recently verified why day two may be so unpleasant.

Like many things, it’s actually all down to hormones.

Specifically, prostaglandins arise when your progesterone levels fall.

They also peak on the second day of your cycle, which explains why the discomfort appears to peak around the same time.

Dr. Fatema Mustansir Dawoodbhoy, an academic doctor specializing in obstetrics and gynaecology who works with the upcoming period care app Joii, told Metro: “As the lining of your uterus breaks down, prostaglandins (hormone-like chemicals) are released in the body.”

According to the expert, extra prostaglandins are regarded to be the primary cause of the horrible cramps you feel on the second day of your period.

Because they stimulate the uterus to contract, ‘helping to shed the old endometrial tissue expelled from your body as period blood’.

She went further: “The prostaglandins also constrict the blood vessels in the uterus, reducing the amount of oxygen the uterine tissue receives, and this leads to cramping and pain.”

Other hormonal changes that occur during the first few days of the menstrual cycle can also influence our sense of pain since, in addition to progesterone, oestrogen levels fall at the start of the cycle.

“This means that other painful conditions like migraines or fibromyalgia can worsen when you have your period, as the hormone oestrogen falls to its lowest level,” Dr Emilie Côté MRCOG, an obstetrics and gynaecology specialist and researcher who also works with Joii, added.

“The second day of the period is typically associated with a heavier menstrual flow for many women,” he told the outlet. “The increased blood volume can lead to more intense cramping and discomfort as the uterus works harder to expel the menstrual blood.”