Experts have warned people against climbing Mount Kilimanjaro as they could be putting their health at risk.
Travel firms have seen an increase in bookings following the successful summit by nine celebrities for last year's Comic Relief campaign.
Edinburgh scientists, who camped for three weeks at the height of 4730m to test altitude sickness in more than 200 climbers, warned that Africa's tallest peak can be fatal.
They assessed climbers using the Lake Louise consensus scoring system, which records symptoms such as headache, sickness and fatigue.
The academics found 47 percent of those who had climbed Kilimanjaro, were suffering from altitude sickness before they reached the summit and most were ascending too high, too quickly.
Signs of sickness include vomiting, headaches, difficulty sleeping and sometimes problems with co-ordination.
Effects can be felt from as low as 2,500m above sea level and 75 percent of people will have mild symptoms at 3,000m or higher, the study said.
"We found that many climbers knew little or nothing about altitude sickness and did not have previous experience of being at high altitude. This research emphasises the need to increase awareness of the risks of altitude sickness and the importance of taking your time to acclimatise," the BBC quoted Stewart Jackson, who conducted the study, as saying.
"Undertaking an acclimatisation trek before attempting to summit Mount Kilimanjaro offers climbers the best chance of a safe, successful summit," he added.
The study is published in the journal High Altitude Medicine and Biology.