A recent study out of Yale indicates that cold air really does cause colds. 

http://www.bbc.com/news/health-30685732

Turns out that about 1 in 6 people carries the common cold virus even without an active, symptomatic cold.  But when the air temperature drops, it causes a drastic drop off in immune response in the nasal passages, so the person with the low-level constant infection suddenly starts broadcasting bigtime as the virus multiplies without an effective immune response.  The recipients are similarly more vulnerable, of course; thus the explosive outbreaks of colds and flu when the temperature drops in the fall.

This echoes a study some years ago that showed that people who worked in cold office areas had a 4X risk for catching a cold or flu.  And, years before that, a study  that showed  a major correlation between hospital deaths and the air temperature in the hospital operating and recovery rooms.  Patients who were operated on had about a 50% better outcome if the operating room was kept warm.  I.e., there were about 50% more deaths when the patients were exposed to cold.

So, the real question then becomes how it is that, armed with this accessible knowledge, doctors and medical facilities continue to maintain unhealthy environments for their patients?  The study regarding hospitals was about a decade old, yet on both occasions when I spent a couple days in the hospital in recent years, the place was COLD!  Of course, it was also filthy and noisy even in the wee hours when patients should be going into a deep healing sleep.  So, perhaps we are drawing the wrong correlation.  Perhaps it is something perversely out of whack in the relationships between caregivers and patients that causes both the cold air and also the other clear indications of neglect.

Recently NPR did a short discussion of the practice of hand washing and how long and hard the discoverer of its value had to fight for general acceptance, while literally millions of not just women in childbirth, but also the surgeons and nurses were dying due to contagion that a simple hand wash stopped in its tracks.  Old history.  Right?  Yet once again the issue is raised as multi-drug-resistant bacteria are spreading like crazy in hospitals - once again provably caused by lack of normal sanitation. The hospitals that have cleaned up their act have been getting far fewer hospital infections.  Yet many have not. 

And, of course, we have the recent nightmarish example of ebola, spread largely by a failure of sanitary practices, down to a lack of simple gloves and masks and soap, because there was no money to pay for them.

A clue may come from the treatments for itching.  In the '60's a team of medical researchers took it upon themselves to investigate a bunch of "old wives tales," apparently simply trying to get a benchmark as to what percentage of what "everybody knows" happens to be false.  The results were published in the then "Discover Magazine," aimed at middle school students.

One such belief was that the best treatment for many common kinds of itching was simply the application of hot water.  This turned out to be the case, and in fact hot water was more effective than just about all the alternatives that people spent big bucks on to treat skin allergies, such as with poison oak.  (They also discovered that some "treatments," such as soaking in cool water with Epson salts, simply made everything much worse, spreading the poison.  And calamine lotions were basically useless.)

Dermatologists today know about this, but still prescribe what brings in the bucks and justifies their existence in the medical/industrial complex. 

Finally, we know now that we were totally WRONG in the way we treated burns through most of the 20th century, and that there is no correlation between eating before swimming and getting stomach cramps.  Nobody checked, because our system does not provide a revenue connection.  Sometimes, as well, there is actual fraud, as when the Red Cross finally admitted that they knew that there was no connection between eating and swimming, after denials for over half a century.  It was just too embarrassing to begin with, and then every additional year added to the guilt.  Think Catholic priests and children.  Scout masters...  What price truth?  Who can name some more?