Holidaymakers are seven times more likely to catch a cold if they travel by air, according to scientists. As many as one in five passengers develops a cold within a week of flying because of bacteria and viruses in the recycled air of the cabin. But catching a cold may be the least of a traveller's worries. Other airborne infections which can be transmitted between passengers include tuberculosis, influenza (flu), measles, mumps and chicken pox.

• Recycled Air. The air is recycled on aircraft and usually consists of 50% fresh and 50% stale air. Boeing Flight Manual. Lufthansa have a mixture of 60% fresh air and 40% recycled whereas other airlines like B.A. have 50-50 or 60-40 of recycled air.
• Bacteria and viruses that cause illnesses like colds flu and pneumonia become airborne when passengers talk cough or sneeze. A cough produces 100,000 particles that can be dispersed over 20 rows in the cabin. This was shown in a study by Boeing and Pall Cabin Filters Brochure 1999.
• Transmission of Disease in flight. Influenza epidemics follow major air routes. The Centres for Disease Control, Atlanta, Georgia has proved that tuberculosis can be transmitted to passengers through the air conditioning. Kenyon T.A. et al (1996). Transmission of multi-drug resistant mycobacterium during a long aeroplane flight. New England Journal of Medicine 4,334. Testimony before subcommittee on Aviation U.S. Senate 1989 Robertson G.
• Severe Acute Respiratory Syndrome.(SARS) As with all infectious diseases,prevention can be controlled by frequent washing of hands. Be alert to symptoms of fever,dry cough,shortness of breath,headache and muscular stiffness.If a respiratory mask is worn the risk of infection can be reduced.
• Gastro-enteritis. Two incidents of gastro-enteritis occurred on a Britannia Flight that affected 46% and 38% of passengers on short flights from U.K. to Europe. The virus was spread directly from person to person and through air conditioning. Public Health Laboratory Services (1997) Donnely m. et al. An investigation of gastrointestinal illness among airline passengers.
• Insecticides (Permethrin). All visitors to Australia are sprayed with pesticides that can cause health problems for passengers with allergies, chemical sensitivities, asthma and other respiratory problems. The pesticide is sprayed either directly into a cabin with passengers onboard or unoccupied cabins are treated with long-lasting residual chemicals. U.S. Consumer Report. Jan 1999. Travel letters