It could be Harry the school hamster, those mouldy copies of The Adventures of Tom Sawyer on the top shelf, or the 29 damp sweatshirts filing into your classroom on a rainy morning that are responsible for your breathing difficulties.

There are more than 5 million asthma sufferers in the UK, and more than half say their working environment can cause problems. Schools are no exception. Whiteboards may have put an end to chalk dust, but what about fumes from marker pens? That is the problem with asthma triggers. There is often a long list of suspects, and fingering the culprits calls for sharp detective work.

Two years ago, Marie Barnes, a primary teacher in the Thames Valley, started suffering asthma attacks in a school where previously she’d had few problems. “It turned out that the cleaners had changed their brand of floor polish and the new one was causing me difficulties. The head was understanding and they switched back immediately.”

Marie admits she was lucky to have her problem taken seriously. Some people think asthma is just a bit of a wheeze. It brings to mind images of children skipping PE and puffing on their inhalers. But anyone who has witnessed or experienced a severe attack knows how frightening it can be.

During an attack, muscles around the walls of the airways tighten, narrowing air passages and inflaming their linings. The result can be mild breathlessness or something much worse. Asthma kills one person in the UK every seven hours.

“Asthmatics can have their condition under control for months or even years,” says Lea Finch, an asthma nurse in Essex. “Then suddenly it flares up and often catches sufferers by surprise.” Even if you have never suffered, it doesn’t mean you never will. It is possible to develop asthma at any time of life. Bear in mind that the number of asthma cases worldwide has doubled in the past decade and that the UK has one of the highest rates of asthma on the planet. What’s to blame? Dirtier air? Or perhaps cleaner houses that make us more susceptible to allergies? No one knows for sure.

Whatever its causes, asthma makes life tough going. For Sarah Hammond, a Harrogate primary teacher, it almost meant the end of her career. “I was spending more time in hospital than at school. Now I wear a steroid drip under my trousers that feeds into my stomach. Even so, I only work two days a week and have a lot of days off work, which makes me feel guilty. The school’s been brilliant about it and accepts that it’s a genuine disability.”

Sarah’s is an extreme case. Most asthmatics can keep things under control using inhalers, while plenty of people swear by homeopathy, vitamin E and even trumpet playing. But the first step to managing asthma is to try to steer clear of the things that trigger it.

If your asthma seems worse at school than during the holidays, then take a look around. One study in Sweden found that open shelving in classrooms increased the incidence of asthma. So get the bursar to splash out on some metal cupboards instead. And while you’re at it, ask about shiny new flooring to replace that old carpet, with its 100,000 dust mites crowding every square metre. Above all, make sure your room is warm, well-ventilated and free of hamsters

Not to be sniffed at

- Serious asthmatics should register as disabled. It protects your job if you need time off.

- See your GP at least once a year.

- Ensure colleagues know how to help out in the event of an attack.

- Play the trumpet or trombone: it strengthens breathing muscles.

Visit www.asthma.org.uk for more information.