Proper acclimatisation to altitudes of 2,500m (just over 8,200 feet) or above is the best way to prevent altitude sickness. Ascending slowly will give your body time to adapt to the change in altitude.

When booking a trip yourself, try to include two or three days to acclimatise. If you're booking a package holiday, check the itineraries of different providers to find a package that allows a few days for acclimatisation. If possible, you should try to avoid flying directly to a high altitude.

Some itineraries are more likely to cause problems with acclimatisation than others. For example, a trekking holiday that involves crossing ridges or low peaks but sleeping in the valleys is less likely to give rise to problems with altitude sickness than a climb up an isolated peak such as Kilimanjaro. 

It's very unusual to get severe altitude sickness during most walking, climbing or skiing holidays to the Alps. Overnight accommodation is usually in valleys or mountain huts at heights of around 3,000m (9,842 feet) above sea level. 

However, acclimatisation for the higher mountains in the Alps will make a successful ascent more likely and safer. Before setting out for peaks over 3,500m (11,482 feet), it's sensible to have spent a few days climbing lower peaks to acclimatise.

It's not only on trekking or climbing holidays that high altitudes are reached – for example, some parts of the Colorado Rockies can be reached by road despite being over 3,500m.

Climb gradually

Once you're above 3,000m (10,000 feet), don't increase the altitude at which you sleep by more than 300-500m a night. You can go up higher during the day, but each night go back down to a camp that's no more than 300-500m higher than the previous night's camp.

Some holiday companies offer trips to climb a mountain in a short space of time, such as climbing Mont Blanc over a couple of days. If you're not already acclimatised, climbing at this rate is likely to lead to symptoms of altitude sickness. It would be better to attempt the climb at the end of a two-week holiday after you've acclimatised by climbing a few lower peaks first.

Medication

To prevent altitude sickness, acetazolamide can be taken twice a day. You should begin taking the medication two days before you start to ascend and should continue to take it while you're ascending. You may also be advised to take it for a day after you've reached your highest altitude.

Dexamethasone isn't usually recommended for preventing altitude sickness, but may be provided for the emergency treatment of high altitude cerebral oedema (HACE).

See treating altitude sickness for more information about acetazolamide and dexamethasone.

Further advice

As well as acclimatising properly and taking prescription medication, you should also follow the advice outlined below.

• If you start to develop mild symptoms of altitude sickness, stay at your current altitude until your symptoms improve.
• If your symptoms get worse, immediately descend from your current altitude.
• Make sure everyone you're travelling with has fully acclimatised before going any higher.
• When ascending above 3,000m, try to have a rest day every three days – this is where you may climb higher, but return to sleep at the same altitude as the night before.
• Keep well hydrated by drinking plenty of fluids.
• Eat a high-calorie diet while at altitude.
• Don't smoke, drink alcohol or use medication such as tranquillisers and sleeping pills while you're at altitude, as they could make any symptoms of altitude sickness worse. Speak to your GP if you're unsure.
• Remember, the risk of sunburn and sunstroke increases at altitude, so take full precautions to prevent them happening. In particular, make sure you have appropriate eye protection – specialist sunglasses, snow goggles or equivalent – and use them to prevent snowblindness, even if it's hazy.