Twenty holiday myths exposed

Can a gin and tonic keep the mozzies away? Does a paper bag prevent jet lag? Kunal Dutta and Lyndsey Fineran get to the truth

Why are school summer holidays so long compared with other breaks?

The long summer break is widely believed to be a throwback to Victorian demands for children to help with the harvest. However, summer holidays didn't match harvest time, as many crops were gathered in in September. State schools only existed post-1870 and holidays were whenever school boards determined they should occur. As teachers were paid by the week, they were reluctant to take a long time off. The historian Jacob Middleton, of Birkbeck College, London, says the long break reflects that enjoyed by the upper classes – in Parliament, the law courts, universities and public schools – which filtered down to urban schools.

If I cut my foot on the beach, can I treat it with sea water?

It is, if anything, the best of a bad set of options. There is some truth that salty water kills bacteria. But most oceans are not sterile environments and there's no knowing what disease you might contract while swimming in tropical waters with an open wound. "Sea water is a stop-gap, but all wounds should be treated in the usual manner: washed, cleaned with antiseptic and appropriately dressed as soon as possible," says Dr Dilanki Ranmuthu, a GP.

Do hanging chains on the back of my car really prevent static?

No. Never did. For years, the chains and rubber "grounding" strips that dangle from bumpers have been sold with the promise of reducing static allegedly picked up by car tyres. Actually, static was rarely generated by anything except clothes rubbing against the car interior. "In the 1980s, there were heaps of driving accessories, and many of us bought into them," said the AA's Vanessa Guyll. "Many said the rubber strips prevented car sickness (and static). They did neither."

Is urine really a cure for a jellyfish bite?

No. According to Joe Mulligan, head of first aid at the British Red Cross: "Slowly pouring seawater over the sting will help ease the pain. Doing the same with vinegar can be even more effective, as the acid helps neutralise the sting. But, unless you're near a chip shop, seawater will probably be easier to find."

Do cold temperatures in a plane cargo hold mean that any bed bugs in your luggage will die en route?

Bed bugs are a lot more resilient than many people give them credit for. They can survive at low temperatures – even below freezing – for significant lengths of time. Unless you are planning on staying in the air for several days, don't rely upon this as a means of decontamination.

Does switching from being out in the sun to an air-conditioned environment cause colds?

No. Though it may be a shock to the system, a change of temperature in itself is not what makes you sick. Colds are caused by viruses that are caught from others. Many germinate on planes, where the poor air quality combined with hundreds of other people in a confined space is a breeding ground for germs. One-fifth of people who fly will come down with a cold a few days later, according to one study.

Can aspirin prevent DVT on flights?

No. Doctors have stopped recommending that long-haul flyers take aspirin to reduce their risk of deep vein-thrombosis. Why? There's no evidence it helps. DVT, which can occur if dehydration and poor circulation combine to trigger a potentially life-threatening blood clot, should instead be prevented by drinking plenty of water, wearing flight socks and taking a walk at least every two hours.

Are cheap sunglasses worse than none at all?

Yes. Specs with UV-protection may be more expensive, but they're absolutely necessary. Sunglasses without UV filters encourage the pupil to open wider, allowing greater amounts of radiation into the eyes. That can make them more risky. "The analogy is with tinted windows on a car: useful for those who want to check people out without being seen. But absolutely no form of other protection beyond delusional vanity," says Dr Ranmuthu.

Does a gin and tonic before bed actually deter mosquitoes?

No. This myth dates back to colonial India, where the British would sink tonic water, which contained quinine, to ward off mosquito-borne malaria. Nowadays, the amount of quinine in tonic is much lower, so minute in fact that it is too risky to rely on it. Creams offer the best protection, particularly as the sun goes down. Research published last week suggested mosquito nets were not as effective as previously believed, although other scientists have challenged this.

Does water go down the plughole clockwise in the northern hemisphere and anti-clockwise in the southern?

Theoretically true, anyone's guess in practice. Named the Coriolis effect, and caused by the Earth's eastward spin, it can affect anything from ocean currents to water going down the plughole. Real bathroom experiments often fail, however, because other factors overcome the effect. The shape of one's bath and the general swirl of bathwater created by getting in and out of the water can result in it travelling in either direction.

Are brown paper bags stuffed in your shoes a cure for jet lag?

No. Nothing more than an old wives' tale. The best cure for jet lag is to set your watch to the destination time from the moment you step on the plane. Drink plenty of fluids and expose yourself to bright light during daytime hours. Brown paper bags, travelling with families, and keeping your mind "blank" are little more than superstitions. Sleeping pills, Viagra and melatonin are listed among the other supposed cures – but their side-effects could be a lot worse.

Bibles in hotel rooms – is it sacrilegious to steal them?

No – in fact it's encouraged! The Gideons, the Nashville-based Christian group, have been delivering Bibles to British hotel rooms since 1949. Provided that permission is granted, the group will deliver scriptures to hotels and periodically replenish supplies. Stealing one, contrary to what you might expect, is anything but sacrilegious. "If someone steals it, which is great, we'll replace it without charge," a spokeswoman in the Gideons' Lutterworth office said.

Can you get on a plane without a passport?

Ignore the tales of bravado from those who say they travelled across Europe with little more than a scrawny driving licence. Airports have little tolerance towards anything except valid photographic ID, while the laissez-faire days of travelling between mainland UK and Ireland have also changed. Even if the airline permits it, expect a frosty reception from border officials. When travelling within the UK, some airlines say that photographic ID in the form of a driving licence can suffice.

Is waterproof sunscreen really waterproof?

No, regardless of what it says on the tin. Even sunscreen products that boast eight-hour protection are not necessarily designed for active holidays. "If you slapped it on and didn't move, perhaps you'd be OK, but those claims should be treated with caution. The fact is that through sweating, rubbing as you move and wiping or towelling down, you'll end up removing as much as 80 per cent of the sunscreen initially applied to your body," says Bevis Man from the British Skin Foundation.

Would that whistle on a lifejacket ever be heard by anyone?

The desperate blow of a whistle in the pitch black may have looked convincing in Titanic. But it is unlikely to lead to a happy ending in real life. You're already in a bad place, and a shrill 1970s whistle doesn't offer any guarantee of being picked up and taken to safety. "Most search-and-rescue teams now have sophisticated technology, including infra-red and heat-seeking cameras, that are more likely to find you than the use of a whistle," says the International Aviation Bureau's Phil Seymour.

Is it true that sitting near the emergency exit gives me the best chance of surviving a plane crash?

According to the International Bureau of Aviation, "most headline-generating crashes result in 100 per cent fatalities so seating arrangements ultimately make little difference". A study by the Civil Aviation Authority revealed that the aisle seats near the front and within five rows of an emergency exit offer more chance of a quick escape in the event of a fire. But, to be realistic, not much more.

Is there anywhere I can sit on a ferry that makes it less likely I'll be seasick?

Seasickness is ultimately a case of mind over matter. Locate the part of the boat with the least movement. Go on deck at the bow (front) end, which allows you to look ahead and anticipate the movement of the boat. "Keep away from the exhaust fumes, which often catch people by surprise," says Beverley Morris, head of Faliraki Sea Lines. Don't read, use binoculars or cameras, as these can add to the unpleasantness. Try to keep the horizon in sight, but don't concentrate or stare at it, and avoid things that your brain would normally consider stable, such as walls and furniture.

Is the advice not to swim immediately after eating an old wives' tale?

The "old wives" knew of what they spoke. Not exercising while your body is still trying to digest food, especially if you've eaten a heavy meal, is basic common sense, say doctors. However, the combination of eating, swimming and drowning as a result is very rare. Studies of athletes have shown that physical activity, including swimming after a meal, does not cause stomach cramps or nausea. In fact, long-distance swimmers sometimes eat while they are still in the water.

Does suncream really lose half its SPF every year past its sell-by date?

Just about. In the wacky world of skin protection, a half-sunk bottle of last year's factor 30 is better than none at all. But don't expect miracles. Dr Tamara Griffiths, spokesman for the British Skin Foundation, says: "There are 'use by' dates on bottles of sunscreen, and tests have shown they are still usable and effective afterwards. However, there is no guarantee that they will be as effective as they were before. It's better to use [out-of-date suncream] than not use any at all."

Do wasps really get irritated if I bat them away?

Yes. Wasps prey on aphids and are attracted to fruit as well as the contents of a picnic basket. A swat not only annoys them, but it heightens the chances of being stung or, worse, the insect returning to the nest and marshalling others for a mass onslaught. "A gentle waft or light puff of air should get one out of your way without irritating it," says Dale Harrison of the charity Buglife.