Once every month, one in three female teachers will be bombarded with a litany of distressing physical and psychological symptoms. It may be "nothing more" than tiredness or bloating, but in its extreme guise, pre-menstrual tension - or syndrome - will leave women completely debilitated.
"Clinically, 90 per cent of women will be affected to some extent," says Christopher Ryan, chief executive of the National Association for Premenstrual Syndrome.
"About 30 per cent will have moderate symptoms for two to three days around the onset of their period. But 8 per cent of women of a reproductive age will have extreme symptoms, which can be entirely debilitating."
It is hard to pinpoint problems directly but sufferers may encounter anything from agoraphobia to depression or migraines - and almost everything in between, with approximately 150 separate symptoms linked to the condition.
It is not known why some women suffer more than others, but the fluctuating levels of hormones experienced after ovulation is almost certainly to blame and some women have lower than normal levels of serotonin (which regulates mood) in the brain post-ovulation.
"For teachers it can be the most awful thing," says Christopher. "They have to stand up in front of all these fractious pupils, who may be hard to control at the best of times, and battle through while feeling very fragile themselves."
Cyclical health problems on this scale can have a major impact on the teaching profession as a whole, says Christopher. "The nature of teaching can be stressful without added complications. It can and does affect people's careers."
Jackie Howard, 62, is a retired primary school teacher from Kent and says that work was a useful distraction, although her PMS could still get the better of her. She kept a chart of her symptoms and controlled some of the unpleasant side effects through diet.
"It's a bit like being a diabetic," she says. "I would suggest eating wholemeal bread and other slow-release carbohydrates such as brown rice, and never go more than eight hours without food. A lot of women think they will put on weight if they snack regularly, but that shouldn't happen if you avoid chocolate and other sugary things."
Regulating lifestyle can also make a difference. Some women find that less alcohol, caffeine and nicotine can help, alongside non-hormonal treatments such as vitamin B6, evening primrose oil or diuretics. The contraceptive pill is often prescribed although there is limited evidence that it actually works in alleviating the symptoms.
The only conclusive way of ditching pre-menstrual tension is to ditch the periods. Lybrel, a new contraceptive pill, can be taken every day without a break and could be the lifeline sufferers are looking for. It completely stops periods and is already available in America and may be coming to the UK later this year.
However, some experts are concerned that it may increase the risk of breast cancer and blood clots. For those who suffer so badly that the only relief would be the surgical removal of their ovaries, it may be a risk worth taking.
How to help yourself
- Keep a menstrual diary for at least two months to trace how your lifestyle affects symptoms.
- Reduce sugar, salt, caffeine and alcohol.
- Increase intake of fruit, vegetables and water.
- Take three-hourly carbohydrate snacks such as rice cakes or crackers.
- Increase exercise.
- Take time to relax.
- Experiment with herbal and alternative treatments such as evening primrose oil.
- Visit www.pms.org.uk for more information.