And the bad news is that classrooms are a viral jungle. "I can't think of a better place to catch a cold," says Professor Ron Eccles of the Common Cold Centre at Cardiff University. "You've got lots of people in a confined space and, in primary schools in particular, children aren't very hygienic. There's a lot of snot going around."
What's more, because their immune systems are still developing, young people average seven or eight colds a year, compared with the three or four that most adults can expect. So there's always likely to be someone in the room who's coughing and spluttering. "Teachers are going to come into contact with cold-causing viruses whether they like it or not," says Professor Eccles.
But if you can't dodge the germs, you can at least discourage colds from taking hold. The first step is to ensure your immune system is in good order. That means regular exercise, plenty of sleep, and a healthy diet. And doing things your mum used to suggest: wash your hands; don't pick your nose; wrap up warm. It is all good advice.
Regular hand-washing cuts the risk of infection. But you can't keep them clean all day, unless you're unhealthily compulsive. So don't touch your eyes, nose or mouth, because viruses enter your body there. The nose is key. Of the 200 or so viruses that cause the sniffling, sneezing, bunged-up feeling we call the common cold, over half are nose-dwellers.
That's why Professor Eccles suggests muffling up on your way to work or out in the playground.
"When your nose cools down it slows the movement of the mucus, and the activity of the white cells. And that lowers your resistance to infection." He claims it is one of the main reasons why colds are more common in winter. So, stick a balaclava on your head.
Or, you could try taking tablets instead. Since the 1950s, Vitamin C has been used to keep colds at bay. However, new research suggests it is not that effective. Echinacea, a daisy-like herb that grows in the US, seems more promising. One recent study shows that it can cut your chances of catching a cold by about 50 per cent.
"I'm definitely a fan," says Alan Bacsich, an English teacher in Sheffield. "I don't use it all year, but sometimes in assembly it seems like the whole school is coughing away. That's when I start taking echinacea. I've been teaching three years and hardly had a sniffle."
Another plant said to prevent colds - with some scientific support - is garlic. You can buy odourless sugar-coated tablets, or you can try eating the real thing. It should help keep those snotty-nosed kids at a more hygienic distance.
- Wash hands regularly. Consider using a long-lasting disinfectant.
- Avoid rubbing your eyes or biting your fingernails.
- Gentle exercise boosts the immune system. Overdoing it has the opposite effect.
- Stay happy. Being stressed or depressed makes you vulnerable to colds.
- If you feel the sniffles coming on, Professor Eccles suggests Vicks First Defence nasal spray. It traps viruses in your nose using a gel, and may stop you developing full-blown symptoms.