Contrary to popular belief, spending time outside in the cold is not why people get sick in the winter.
People don't actually get sick colds and the flu because of cold weather.
People are more likely to get sick during wintertime because they spend more time indoors and they share more germs because of it, causing them to get sick more often. There is also evidence now that viruses spread more easily through dry air. When it is cold outside, the air is drier both outdoors and inside. In tropical areas, the common cold and flu season generally occurs during the rainy season because people come in closer contact with each other indoors.