"Cold" as misnomer
If cold weather were directly linked to the spread of the common cold, then it could possibly be demonstrated by comparing the infection rates of people who live in colder climates (such as Iceland or Greenland) with people who live in warmer climates (such as countries close to the equator). Studies done in the 1960s found no significant increase in infection rates in people who live in colder climates.
It is not known conclusively whether cold weather or a humid climate can affect transmission by other means, such as by affecting the immune system, or ICAM-1 receptor concentration, or simply increasing the amount and frequency of nasal secretions and frequency of hand to face contact. A person can best avoid colds by avoiding those who are ill and the objects that they touch, as well as by keeping their immune system in top form by getting enough sleep, reducing stress, eating nutritious foods, and avoiding excess alcohol consumption. However, researchers at the Common Cold Centre at the Cardiff University demonstrated in 2005 that cold temperatures can lead to a greater susceptibility to viral infection. They showed that a group of people who sat with their feet in cold water for 20 minutes a day for a week had a 1 in 3 chance of developing cold symptoms during that week, while a control group who were not exposed to the chill had a 1 in 10 chance. It is thought this may be due to cold temperatures reducing blood circulation needed to carry white blood cells to the area of infection.
However according to Dr. Ronald Turner the study is fatally flawed because the researchers failed to check whether the participants were already infected or not. Other more controlled studies have failed to find a link between low temperatures and infection.