People with angina, for example, may find they experience chest pains because the heart isn't getting enough oxygen, or those with asthma or chronic obstructive pulmonary disease may find their breathing a little harder or wheezy.

At aircraft cabin pressure the air in body cavities expands. Favourite places for this to happen are the ears, sinuses and teeth, if tooth decay has caused erosion. The result is severe pain.

The air quality in a plane in general is not as good as the air outside, and the air filters are not always fully effective. This allows bacteria and viruses to spread very easily from one person to another, which is why many people come home from their vacation with a cough or a cold.

Also, the air isn't humidified, which contributes to the body becoming dehydrated. This and the drying out of the protective mucosa of the mouth and nose, which would normally act as a barrier to bacteria and viruses, increases susceptibility to infection.

Travelling by plane when you have a cold can cause permanent ear or sinus damage. Ideally, you should wait until your condition improves, particularly if you have a high fever or ear/sinus pain. Consult your doctor about whether it's safe for you to travel - she may be able to prescribe antibiotics or decongestants.

Changes in air pressure when an aircraft is ascending or descending may cause discomfort for travellers with a head cold or ear condition. Pinch the nose and, with the mouth shut, blow out gently. Swallowing, chewing gum or sucking sweets can also help.

If you've recently been treated for an ear condition, you should wait at least two weeks before travelling by air.

Travellers with a history of motion sickness or sea sickness can attempt to avoid symptoms by taking anti-motion-sickness pills before departure. As with any medication, consult your GP for specific advice.

Preventing problems Allow plenty of time to get to and through the airport. Things do go wrong so plan for this. Make use of luggage trolleys and ask for help from the airport staff, if you're having difficulty. It's better to share a load than to end up with strained muscles.

Drink plenty of water during the flight. One or two glasses an hour is a good guide. It's best to avoid alcohol and caffeinated drinks during the flight since they contribute to dehydration.

Every hour get up and out of your seat and move around for about ten minutes

Swollen feet, aching joints and muscles, stomach pain from indigestion and wind all result from immobility. Every hour get up and out of your seat and move around for about ten minutes. Have a good stretch too.

During the flight, particularly while taking off and landing, suck sweets, swallow or hold your nose and try to blow out. This will equalise the pressure and help avoid ear and sinus pain.

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