When it is cold, your body spend a lot of energy to sustain body temperature, lowering the immunity. Also, temperature inside your nose lowers, so protection mechanisms works worse. So, it is easier for pathogens to do harm.
From the other side, sun is not only source of UV which destroys pathogens, but also a necessary ingridient of vitamin D synthesis. And vitamin D plays big role in immunity.
Immunity is not very fast, so, coming back home from the cold outside does not immidiately activate lowered by cold immunity, and pathogens have more time to attack.
It will be interesting to take a look at influenza statistics for equatorial countries with negligible seasonal temperature variations and compare it with higher latitudes vhere variations are huge.
Interesting, that usually I more probably catch a flu not at extremely cold weather (I hardly remember if I ever get ill at -30°C outside), but when it is moderate cold (-0°C - -15°C) and wet. When it is warm, I could get only tonsillitis after a tons of ice cream, independent of humidity.
When it is cold, your body spend a lot of energy to sustain body temperature, lowering the immunity. Also, temperature inside your nose lowers, so protection mechanisms works worse. So, it is easier for pathogens to do harm.
From the other side, sun is not only source of UV which destroys pathogens, but also a necessary ingridient of vitamin D synthesis. And vitamin D plays big role in immunity.
Immunity is not very fast, so, coming back home from the cold outside does not immidiately activate lowered by cold immunity, and pathogens have more time to attack.
It will be interesting to take a look at influenza statistics for equatorial countries with negligible seasonal temperature variations and compare it with higher latitudes vhere variations are huge.
Interesting, that usually I more probably catch a flu not at extremely cold weather (I hardly remember if I ever get ill at -30°C outside), but when it is moderate cold (-0°C - -15°C) and wet. When it is warm, I could get only tonsillitis after a tons of ice cream, independent of humidity.