|A perfect day for us; hell for pathogens. |
Source: Mantas Volungevicius
But what about scientific evidence? An early study about the effects of fresh air on pathogens came from the height of the Cold War, in the 1960s. Biological warfare was a real concern, so microbiologists wondered how long the microbes would stay viable. When they exposed E. coli bacteria to fresh air, all of them were dead within two hours, but controls kept in boxes at the same temperature and humidity mostly survived. They called the mystery ingredient the "open air factor". This mystery factor turns out to be hydroxyl free radicals; while they aren't harmful to larger organisms such as humans, they are deadly to tiny bacteria. However, the open air factor rapidly disappears with increasing degrees of seclusion (The Influence of Sunlight and Ventilation on Indoor Health: Infection Control for the Post-Antibiotic Era). Later research showed that the risk of respiratory infections was 50% higher in US Army recruits who slept in newer barracks, where the windows were more likely to be closed and the air was recirculated more than in the older ones. Another US study in a jail found that during an outbreak of pneumococcal disease, infection rates were 95% higher in cells with the lowest amount of outside air supply. In research on Chinese university students, 35% of students caught at least 6 colds per year if the ventilation rate was one litre per second per person. If the ventilation rate was 5 litres (per second, per person), then only 5% caught at least 6 colds per year.
As for sunlight, we now know that it triggers our production of vitamin D, which has many health benefits such as boosting our immune system. Older research, dating back to the 1870s at the earliest, showed that sunlight can also directly kill bacteria. Robert Koch was the first to announce that sunlight kills the tuberculosis bacteria, and studies in the 1940s found that areas of TB wards exposed to sunlight tested negative for the bacteria, which did not survive more than a few days. Spaces such as the inside of drawers and refrigerators allowed them to survive for months. Even though we now know that excessive sunlight can cause skin damage, spending time in the sun is necessary, as long as it is not enough to burn at all. Overall, we do not have to be at the mercy (or lack thereof) of dangerous bacteria; they have weaknesses that strengthen us.