Airline passengers 'seven times more likely to catch a cold' Scientists in California claim holidaymakers are seven times more likely to catch a cold if they travel by air. The US study of 1,000 passengers found 21% caught colds within seven days of taking a flight. The Daily Mail reports the team studied passengers who flew on planes where 50% of the air is recirculated, and planes using 100% fresh air such as Concorde. Researchers at the University of California found no difference in risk on planes which recirculate air in cabins. Professor John Balmes, said: "Filters used on planes with recirculated air are designed to filter out dangerous particles, and they may be doing a good job. "It may be that just being on a packed plane is the primary factor, or maybe travelling is the issue - changing time zones and losing sleep." Professor Balmes, who led the study, has advised airline passengers to wash themselves after shaking hands and avoid touching their nose. They found 21% of airline passengers caught colds, compared to an average 3% of the general population. Health campaigners say low humidity levels on board aircraft are to blame for the increased risk of infection.