Premenstrual mood disorder
Some women suffer physical, psychological and behavioural symptoms - PMS - ahead of their period. But one psychologist has claimed it's just a myth. iStock

Premenstrual syndrome (PMS) affects most women at some point during their lives, both physically and psychologically. It can make women feel irritable and depressed, giving them bloating, cramps or other intense symptoms.

But now psychologist Robyn Stein DeLuca, who has written a book about how PMS "keeps women down", has claimed it is just a myth and a "get out of jail free" card women can use as an excuse to have a break.

Speaking to the Mail Online about her book The Hormone Myth, DeLuca said: "Women are expected to do a lot of things these days — we work, take care of families, we make sure everyone's health is OK, we make the Christmas dinner and a lot of women use PMS as a release valve or if they just can't give any more.

"You lose your good woman crown if you say: 'I just don't feel like doing this right now,' and relinquish your responsibilities. But if you say it's PMS, it's like a get-out-of-jail-free card. It's women's excuse for when they need a break."

DeLuca added that the "myth" is that PMS affects woman emotionally "to the point that it's a big deal", but did admit women can get symptoms such as cramps, bloating and depression. She claimed that only 3-8% of women are actually affected by PMS and changing hormone levels, not the commonly cited 90%.

But what actually is PMS, and why do so many women suffer from it?

The NHS says typical symptoms – which encompass physical, psychological and behavioural issues – are bloating, breast pain, mood swings, feeling irritable and loss of interest in sex. These normally appear in the two weeks leading up to a women's period and improve when menstruation begins.

People often joke about PMS being the cause of a woman being moody or weepy, perhaps without realising its prevalence in women's lives. Monash University in Australia found that 90% of women experience at least one symptom most months, and 50% of women regularly get several symptoms. This includes nearly all women of childbearing age, but particularly those in their late 20s to their early 40s.

Around one in 20 women suffer enough to have their normal lives interrupted by severe symptoms – this is often the result of a more intense type of PMS, premenstrual dysphoric disorder (PMDD), and can be managed by a doctor. According to Monash University, this is what actually affects 3-8% of women.

The reason people are still able to say that PMS is just a myth may be that its exact cause is not fully understood. DeLuca claimed there is scientific evidence that fluctuating hormone levels do not "mentally destabilise" us.

But PMS is widely thought to be linked to the changing levels of hormones in a woman's body during her menstrual cycle, when levels of hormones such as oestrogen and progesterone rise and fall. The change is triggered by the release of an egg by the ovary each month, after which progesterone is passed into the bloodstream. It is thought that women with PMS are more sensitive to normal levels of progesterone.

Another theory is that changes in hormone levels during the menstrual cycle can affect the levels of some chemicals in the brain such as serotonin, which is known to help regulate mood and make people feel happier. This is why, for some severe PMS sufferers, an antidepressant that increases serotonin levels improves their symptoms.